Planning, Scheduling and Production Control

Introduction

Construction projects convert designs, materials, labour, equipment and information into a physical facility under conditions of uncertainty. Planning determines what must be done and how the work will be organized; scheduling determines when activities will occur; production control compares actual performance with the plan and initiates corrective action. These functions are closely connected. A schedule without a realistic production plan is merely a date list, while production control without a baseline lacks a reliable standard for comparison.

Construction planning operates at several levels. Strategic planning establishes project objectives, contracting strategy, major methods and resource policies. Project planning converts the scope into work packages and defines logical relationships. Short-term planning coordinates crews, materials, access and information. Daily production control measures actual work, identifies constraints and protects reliable workflow.

The construction manager must balance the project objectives of time, cost, quality, safety and sustainability. Acceleration may reduce time but increase cost or risk. A highly efficient sequence may be unacceptable if it creates unsafe congestion. Consequently, planning is both a technical and managerial discipline.

Learning Objectives

By the end of this chapter, students should be able to:

1. Develop a work breakdown structure and relate it to control accounts and work packages.
2. Construct and interpret precedence-network diagrams.
3. Calculate early and late activity times, float and the critical path.
4. Prepare resource plans and recognize resource-constrained scheduling issues.
5. Establish progress baselines and use productivity measures and earned value.
6. Apply lean construction, pull planning and the Last Planner System.
7. Diagnose schedule and production problems and recommend corrective action.
8. Evaluate the ethical, contractual and technological implications of production control.

1. Planning as a Production System

A construction project can be viewed as a temporary production system. Inputs include drawings, approvals, labour, equipment, materials, money and information. Processes include procurement, fabrication, installation, inspection and commissioning. Outputs include completed work, records and facilities. Variability enters through weather, design changes, late deliveries, rework, labour availability and differing site conditions.

A sound plan answers five questions:

• What work is required?
• In what sequence must it occur?
• How long should each activity take?
• What resources and information are required?
• How will performance be measured and corrected?

Planning should be progressively developed. Early estimates use limited information and broad assumptions. As design and procurement information improves, activities are decomposed, durations are revised and constraints are removed. This progressive refinement should not be confused with uncontrolled change: assumptions and revisions must be documented through formal change control.

Planning horizons

2. Work Breakdown Structures

A work breakdown structure (WBS) is a hierarchical decomposition of the total project scope into manageable components. It is deliverable-oriented: it describes what must be produced, not merely the organization of the contractor. The highest level represents the project, and successive levels divide it into systems, areas, disciplines, control accounts and work packages.

The WBS should satisfy the 100 percent rule: the lower-level elements collectively represent all the authorized scope of the parent element, without unplanned overlap. A useful work package is sufficiently small to estimate, assign, schedule, budget, execute and measure, but not so small that administration overwhelms production.

For example, a building WBS may contain:

1. Project management and general conditions
2. Site development
3. Substructure
4. Superstructure
5. Building envelope
6. Mechanical systems
7. Electrical systems
8. Interior finishes
9. Testing, commissioning and handover

Each element can be decomposed further. “Substructure” might include excavation, shoring, foundations, waterproofing and backfill. A work package should have a defined scope, responsible party, planned duration, budget, predecessor and successor relationships, quality requirements and acceptance criteria.

The WBS is not the same as a schedule. The WBS organizes scope; the schedule places activities in time. It is also not identical to an organizational breakdown structure, which identifies responsibility by company or department. A coding structure can connect WBS elements with cost accounts, locations, trades and schedule activities.

Planning from the WBS

A practical development sequence is:

1. Confirm contract scope, drawings, specifications and exclusions.
2. Identify major deliverables and project milestones.
3. Decompose deliverables by system, location, trade or construction process.
4. Define work packages with measurable completion criteria.
5. Assign responsibility and cost accounts.
6. Convert work packages into schedule activities.
7. Verify interfaces, temporary works, inspections, permits and handoffs.
8. Review the structure with those who will execute the work.

Poor decomposition creates common problems. Overly broad activities conceal delay and make progress subjective. Excessively detailed activities create a fragile schedule with high updating effort. Missing temporary works, testing, approvals or commissioning produces an apparently complete but operationally unusable plan.

3. Network Scheduling and the Critical Path Method

A network schedule represents logical relationships among activities. An activity is a defined amount of work with a duration and usually a resource requirement. A network event or milestone marks a point in time but consumes no duration. Most modern construction schedules use activity-on-node representations, in which boxes represent activities and arrows represent relationships.

The most common relationship is finish-to-start (FS): successor activity B cannot start until predecessor A finishes. Other relationships include start-to-start (SS), finish-to-finish (FF) and start-to-finish (SF). Lags may be used when a time interval is required, but excessive use of lags can conceal real work and weaken schedule transparency.

The critical path method (CPM) calculates the longest time-path through a network. Activities on a critical path generally have zero total float under the selected calculation convention. Delay to a critical activity can delay project completion unless a recovery action changes the network, duration or logic. A project can have more than one critical path, and criticality can change as actual progress and remaining durations change.

CPM calculations

For activity i, let:

• ESᵢ = early start,
• EFᵢ = early finish,
• LSᵢ = late start,
• LFᵢ = late finish,
• dᵢ = activity duration.

Using a time origin of zero, the forward-pass relationships are:

For an activity with predecessors P:

If an activity has no predecessor, ESᵢ is normally zero. For a project completion milestone with required completion time T, the backward pass is:

For an activity with successors S:

For the final activity or milestone, LF is set to the required project completion time, often the calculated earliest completion in an unconstrained CPM network. Total float is:

All times must use the same unit, such as working days. These equations assume fixed activity durations, specified logical relationships and a precedence network without resource limitations. CPM identifies logical schedule flexibility; it does not by itself guarantee that labour, equipment, space or materials are available.

Worked example: a precedence network

Consider the following activities:

Forward pass:

• A: ES = 0, EF = 3.
• B: ES = 3, EF = 7.
• C: ES = 3, EF = 8.
• D: ES = 7, EF = 13.
• E: ES = 13, EF = 15.
• F: ES = max(8, 15) = 15, EF = 17.
• G: ES = 17, EF = 24.

The planned project duration is 24 working days. The controlling path is A–B–D–E–F–G, with duration 3 + 4 + 6 + 2 + 2 + 7 = 24 days. Activity C has one day of logical float because it finishes at day 8 while F cannot start before day 15 and is controlled by E finishing at day 15. A one-day delay to C, if it does not exceed the available float, does not necessarily delay project completion; a delay to E directly affects F and therefore G.

CPM results must be interpreted rather than followed mechanically. If the crew assigned to D is moved to another activity, the assumed duration may no longer be valid. If C and D require the same restricted work area, a resource conflict may introduce an additional relationship not shown in the original network.

4. Durations, Uncertainty and Schedule Quality

Activity durations should be based on quantities, production rates, crew composition, work conditions, learning effects and allowances for normal interruptions. A basic production relationship is:

where d is duration, Q is quantity of work and R is production rate in quantity per unit time. If 480 m² of formwork is installed at 60 m² per crew-day, the calculated duration is 8 crew-days. If two equivalent crews can work independently without interference, the elapsed duration may approach 4 days, but this assumption must be tested for access, supervision, materials and workspace.

Production rates should not be copied uncritically from historical data. Weather, congestion, height, shift pattern, crew skill, rework and inspection delays affect actual output. A rate is meaningful only when its quantity definition and conditions are clear.

When uncertainty is significant, three-point estimating may be used. Let a be the optimistic duration, m the most likely duration and b the pessimistic duration. The traditional beta-weighted estimate is:

An associated approximate variance is:

These expressions are planning approximations, not guarantees. They assume a suitably represented range and are most useful for risk analysis rather than false precision. Correlation between activity risks, such as a common permit delay, must be considered; simply adding independent variances can be misleading.

Schedule quality includes realistic logic, clear calendars, measurable activities, documented assumptions, appropriate constraints, visible procurement and approval activities, and consistency between schedule, budget and execution method. Excessive date constraints can produce an attractive but non-diagnostic schedule because they suppress the natural logic of the network.

5. Resource Planning and Leveling

A schedule is feasible only if the required resources can be supplied when needed. Resource planning identifies labour trades, equipment, materials, temporary facilities, workspace, information and cash requirements. Resource loading assigns resource quantities to activities; a time-phased resource histogram shows demand by period.

Resource smoothing adjusts noncritical activities within available float to reduce peaks while preserving the completion date. Resource leveling allows the completion date or activity sequence to change when resources are limited. The distinction is important: smoothing seeks a better distribution within existing flexibility, whereas leveling resolves an actual capacity conflict.

A resource plan should address:

• crew size, productivity and shift pattern;
• equipment availability, capacity and maintenance;
• procurement lead times and minimum order quantities;
• storage, lifting and site access;
• permits, inspections and design information;
• subcontractor interfaces;
• safety, fatigue and environmental controls.

A mathematically optimal resource schedule may be operationally poor if it creates excessive trade stacking or unsafe congestion. Resource decisions should therefore be reviewed with supervisors and workers who understand the physical workface.

6. Baselines and Progress Measurement

A baseline is an approved reference plan against which performance is evaluated. The schedule baseline contains planned dates and logic; the cost baseline contains time-phased budgets; the integrated performance measurement baseline connects scope, time and budget. Baselines should be controlled, not silently overwritten. Approved changes require documented revision, while current forecasts remain distinguishable from the original commitment.

Progress measurement should be objective and tied to physical completion. Suitable methods include installed quantities, milestone weighting, apportioned effort and weighted steps. The simple passage of time is not a reliable measure of construction progress. For example, claiming 90 percent completion because 90 percent of the planned duration has elapsed ignores whether the installed work is actually 90 percent complete.

Productivity measures

Labour productivity can be expressed as output per labour-hour:

where P is productivity, Q is accepted output and H is labour-hours. An alternative is labour input per unit of output:

P and I are reciprocals when measured on the same basis. Units must be stated, such as m³ per labour-hour or labour-hours per m³. Output should normally mean accepted work, not merely activity that has been started. Comparisons require consistent definitions, crew boundaries and working conditions.

Earned value management

Earned value management (EVM) integrates scope, schedule and cost. The principal quantities are:

• Planned Value (PV): budgeted value of work scheduled by a status date.
• Earned Value (EV): budgeted value of work actually completed by that date.
• Actual Cost (AC): actual cost incurred for the completed work by that date.
• Budget at Completion (BAC): total approved budget for the scope.

The schedule variance and cost variance are:

The schedule performance index and cost performance index are:

PV, EV and AC must use the same monetary basis and status date. SV and CV are expressed in currency units, although SV is a value-based schedule indicator rather than a direct number of days. SPI and CPI are dimensionless. Values greater than 1 generally indicate favourable performance for the selected measure; values below 1 indicate less earned value than planned or more cost than earned value, respectively.

A common estimate at completion is:

This assumes current cost efficiency will continue and is not appropriate when the remaining work has materially different risks. Another form is:

which assumes past cost variance is atypical and remaining work will follow the original budget. Forecasts must state their assumptions.

#### Worked EVM example

Suppose BAC = $1,000,000. At the status date, PV = $400,000, EV = $360,000 and AC = $450,000. Then:

• SV = $360,000 − $400,000 = −$40,000.
• CV = $360,000 − $450,000 = −$90,000.
• SPI = $360,000 ÷ $400,000 = 0.90.
• CPI = $360,000 ÷ $450,000 = 0.80.

The project has earned less work than planned and has spent more than the budgeted value of that work. If the current CPI continues, EAC = $1,000,000 ÷ 0.80 = $1,250,000. This is a forecast, not a financial certainty. The manager should investigate quantities, rework, procurement inflation, incorrect budgets and coding errors before authorizing corrective action.

EVM has limitations. It may report a favourable result when a poorly chosen activity earns value early, while critical-path delay remains hidden. Therefore EVM should be combined with schedule-network analysis, physical progress, quality indicators, safety performance and forecast completion dates.

7. Lean Construction and Reliable Workflow

Lean construction adapts lean production principles to the uncertainty and project-based nature of construction. Its central concern is the reliable flow of value-creating work and the reduction of waste. Common forms of waste include waiting, excess movement, transportation, overproduction, inventory, defects, unnecessary processing and underuse of people’s knowledge.

Lean does not mean simply working faster or reducing labour. It means improving the system so that work is released at the right time, information is reliable, materials arrive when needed and problems are exposed early. Examples include standardized work, visual management, prefabrication, reliable handoffs, daily coordination and root-cause analysis.

Pull planning

Traditional planning often pushes activities forward from an assumed start date. Pull planning begins with a required milestone, such as commissioning or owner occupancy, and works backward with the people responsible for delivering the work. Participants identify the conditions and predecessor work required for each milestone. The resulting sequence is tested against procurement, design, approvals, access and handoffs.

Pull planning is not merely a meeting with adhesive notes. It is a collaborative method for making production logic explicit. The plan should be converted into a controlled schedule, with constraints and commitments recorded in a form that can be updated.

The Last Planner System

The Last Planner System (LPS) is a production-planning and control approach that emphasizes the reliability of commitments made by those closest to the work. Its commonly described components are:

1. Should plan: the master and phase schedule describe required outcomes and sequence.
2. Can plan: look-ahead planning identifies and removes constraints so work becomes ready.
3. Will plan: the weekly work plan records realistic commitments by responsible planners.
4. Did plan: completed commitments are reviewed and reasons for variance are investigated.

A frequently used reliability measure is Percent Plan Complete (PPC):

PPC is useful only when commitments are clearly defined and measured consistently. A high PPC can be misleading if commitments are made too easily, while a low PPC can reflect unresolved design or procurement constraints rather than poor crew performance. The key learning is the reason for noncompletion, such as predecessor work incomplete, material unavailable, design information late, labour shortage or unforeseen condition.

LPS complements rather than replaces CPM. CPM provides a project-level model of dates and logic; LPS manages the reliability of near-term production. A project needs both strategic coordination and dependable workface commitments.

8. Production Control and Corrective Action

Production control follows a cycle:

1. Establish the approved plan and measurable baseline.
2. Observe actual quantities, dates, costs, quality and constraints.
3. Compare actual performance with planned performance.
4. Diagnose the system cause of variance.
5. Select and authorize corrective action.
6. Implement, communicate and monitor the response.

Corrective actions may include resequencing, adding a qualified crew, changing a method, expediting materials, releasing design information, removing access restrictions, reducing rework or negotiating an approved scope change. “Add labour” is not a universal solution. On a congested site it may lower productivity, increase safety risk and create more interference.

A useful control meeting distinguishes facts from explanations. “Thirty metres of pipe installed against forty planned” is a fact. “The crew was unproductive” is an interpretation requiring evidence. A better diagnosis examines crew availability, workface readiness, drawings, materials, equipment, predecessor completion and inspection release.

9. Illustrative Case: Delayed Hospital Fit-Out

Background

The following is a fictional illustrative case. A hospital fit-out has a contractual completion milestone in 20 weeks. The master schedule shows mechanical rough-in, electrical rough-in, partitions, ceiling systems, finishes, testing and commissioning. The project uses CPM for the master schedule and weekly coordination meetings for trade commitments.

Problem

At week 10, the schedule reports an SPI of 0.86 and the ceiling installation date is forecast to slip by two weeks. The project team proposes adding a second ceiling crew. However, the work area is congested, several fire-stopping details are awaiting approval, and mechanical ductwork is incomplete in three zones.

Analysis

A review of the network shows that ceiling installation is not the primary cause. The controlling sequence is delayed mechanical completion followed by inspection and fire-stopping release. The extra ceiling crew cannot create productive work because the workface is not ready. A PPC review shows that only 65 percent of weekly commitments were completed. The main reasons are late drawings, incomplete predecessor work and material delivery errors.

EVM indicates a cost problem, but the team verifies that some costs were coded to the fit-out package before the corresponding work was accepted. Thus the cost index requires interpretation rather than immediate blame. Physical quantities and accepted inspection records are used to correct the performance picture.

Approach and solution

The team conducts a pull-planning session from the commissioning milestone. It divides the floor into zones, defines handoff criteria and assigns responsible parties. A six-week look-ahead plan identifies fire-stopping details, duct pressure testing, inspection requests and ceiling-material delivery as constraints. The design manager commits to release details by specified dates; the mechanical subcontractor commits to zone-based completion; the superintendent limits trade access to prepared workfaces.

The weekly plan includes only work that is “can-do”—that is, work with the necessary design, materials, labour, access and predecessor conditions. Reasons for missed commitments are recorded without disguising them through schedule rebaselining. A small additional crew is added only after two zones become ready.

Outcome

After three weeks, PPC rises from 65 percent to 87 percent, and the forecast delay falls from two weeks to three working days. Productivity improves because crews spend less time waiting and relocating. The remaining delay is reported transparently and managed through an approved resequencing agreement.

Learning points

• A critical activity may be a symptom rather than the root cause of delay.
• Resource additions are effective only when workfaces are ready.
• Constraint removal is often more valuable than overtime.
• EVM, CPM, physical progress and LPS indicators answer different questions.
• Reliable commitments require psychological safety: teams must be able to report constraints without being pressured into unrealistic promises.

10. Digital Tools, AI and Governance

Scheduling software can calculate networks, produce resource histograms, integrate cost codes and compare updates with baselines. Building information modelling can connect activities to locations and components, supporting four-dimensional visualization. Field applications can capture quantities, photographs, inspection records and daily labour hours.

Artificial intelligence and machine learning may assist with schedule-risk prediction, image-based progress measurement, document classification and productivity analysis. Their outputs remain dependent on data quality and consistent definitions. An algorithm trained on one project may not transfer reliably to another with different trades, contract terms or site constraints. AI-generated forecasts should be explainable, checked by competent professionals and never used to conceal uncertainty or unfairly penalize workers.

Governance requirements include version control, access permissions, audit trails, cybersecurity, privacy and contractual ownership of project data. Progress images may contain identifiable workers or sensitive facility information. Automated productivity monitoring can damage trust if used for surveillance without a legitimate purpose, transparency and appropriate safeguards.

11. Challenges, Limitations and Professional Judgment

Planning models simplify reality. CPM commonly assumes deterministic durations and stable logic, but construction contains weather risk, design evolution, learning effects and correlated disruptions. EVM can create misleading confidence if budgets are poorly structured or progress rules are subjective. PPC may be manipulated through weak commitments. Resource histograms may ignore workspace and safety. Lean tools can become superficial rituals if managers demand numerical compliance without removing constraints.

Professional judgment is therefore essential. Planners should make assumptions explicit, use ranges where uncertainty matters, validate plans with constructors and update forecasts without rewriting history. Contractual obligations must be respected: unauthorized acceleration, inaccurate reporting or concealment of delay may create legal and ethical consequences. Progress claims should reflect verifiable work, and schedule updates should not be altered to misrepresent responsibility.

Best practice is to integrate several views:

• Scope: Is the required deliverable clearly defined?
• Logic: Are dependencies and handoffs realistic?
• Resources: Can the work be executed safely with available capacity?
• Readiness: Are design, materials, access and approvals available?
• Performance: What do quantities, productivity, EVM and PPC show?
• Forecast: What is now likely to happen, and what decision is needed?

Chapter Summary

Planning, scheduling and production control form an integrated management system. The WBS decomposes complete project scope into accountable work packages. Network scheduling expresses logical relationships, while CPM calculates early dates, late dates, float and critical paths under stated assumptions. Duration estimates should be connected to quantities and production rates, and uncertainty should be recognized rather than hidden.

Resource planning tests whether the schedule is executable. Baselines provide controlled references for time, cost and scope. Productivity measures describe the relationship between accepted output and labour input. EVM compares planned value, earned value and actual cost, but it should be combined with physical progress and critical-path analysis.

Lean construction focuses on reliable flow and waste reduction. Pull planning works backward from required milestones, and the Last Planner System connects master planning with constraint removal, weekly commitments and learning from noncompletion. Effective production control diagnoses causes rather than blaming crews or applying indiscriminate overtime. Digital tools and AI can improve visibility, but data quality, professional judgment, ethics and governance remain essential.

Key Terms

Baseline: Approved reference plan used to compare actual performance.

Critical path: Longest logical path through a network, controlling calculated project duration.

Earned Value (EV): Budgeted value of work actually completed by a status date.

Finish-to-start relationship: Logic in which a successor cannot start until its predecessor finishes.

Float: Allowable schedule movement without violating a defined completion or successor constraint.

Last Planner System: Collaborative production-control approach based on reliable commitments and constraint removal.

Look-ahead plan: Near-term plan used to identify and remove constraints.

Planned Value (PV): Budgeted value of work scheduled by a status date.

Percent Plan Complete (PPC): Percentage of planned commitments completed as promised.

Predecessor: Activity or condition that logically comes before another activity.

Production control: Measurement and correction of work execution against an established plan.

Productivity: Output produced per unit of input, such as quantity per labour-hour.

Pull planning: Collaborative planning performed backward from a required milestone.

Resource leveling: Adjusting a schedule to resolve resource limitations, possibly changing completion dates.

Resource smoothing: Redistributing work within available float to reduce resource peaks.

Schedule Performance Index (SPI): Ratio of earned value to planned value.

Work package: Manageable, measurable portion of project scope assigned for execution and control.

Work Breakdown Structure (WBS): Hierarchical decomposition of total project scope.

Review Questions

Short Answer Questions

1. What is the purpose of a work breakdown structure?
2. Distinguish resource smoothing from resource leveling.
3. Define total float in a CPM network.
4. What does a PPC value measure?
5. Why should EVM be combined with physical progress measurement?

Long Answer Questions

1. Explain how a WBS is developed and how it connects scope, schedule and cost control.
2. Describe the forward-pass and backward-pass procedures in CPM, including their assumptions.
3. Explain how resource availability and workspace constraints can change a logical schedule.
4. Discuss the principles of lean construction, pull planning and the Last Planner System.
5. Evaluate the usefulness and limitations of EVM for controlling a complex construction project.

Analytical / Application Questions

1. A project has BAC = $800,000, PV = $300,000, EV = $270,000 and AC = $360,000. Calculate SV, CV, SPI and CPI, then interpret the results.
2. A work package contains 900 m² of blockwork. One crew installs 45 m² per crew-day. Determine the theoretical duration for one crew and discuss at least three conditions that could make the actual elapsed duration different.
3. A weekly plan has 24 commitments, of which 18 are completed. Classify the PPC result and propose a structured investigation into the six missed commitments.

Multiple Choice Questions with Answers

Question 1

Which statement best describes a work breakdown structure?

A. A hierarchy that decomposes total project scope into manageable deliverables and work packages

B. A list of workers arranged by organizational rank

C. A cash-flow forecast arranged by accounting period

D. A network showing only activities on the critical path

Correct Answer: A. A hierarchy that decomposes total project scope into manageable deliverables and work packages

Question 2

In CPM, an activity has ES = 6 days and duration = 4 days. What is its EF?

A. 2 days

B. 4 days

C. 10 days

D. 24 days

Correct Answer: C. 10 days

Question 3

For an activity with ES = 8 days and LS = 11 days, assuming the same total-float convention, total float is:

A. 3 days

B. 8 days

C. 11 days

D. 19 days

Correct Answer: A. 3 days

Question 4

Which relationship means that a successor cannot start until its predecessor finishes?

A. Start-to-start

B. Finish-to-start

C. Finish-to-finish

D. Start-to-finish

Correct Answer: B. Finish-to-start

Question 5

If EV = $360,000 and PV = $400,000, the schedule performance index is:

A. 0.80

B. 0.90

C. 1.11

D. $40,000

Correct Answer: B. 0.90

Question 6

If EV = $360,000 and AC = $450,000, which interpretation is correct?

A. CPI is 1.25, indicating cost efficiency above plan

B. CPI is 0.80, indicating less value was earned per dollar spent

C. CPI is 0.90, indicating schedule delay only

D. CPI is $90,000, indicating the project is ahead of budget

Correct Answer: B. CPI is 0.80, indicating less value was earned per dollar spent

Question 7

What is the principal purpose of look-ahead planning in the Last Planner System?

A. To remove constraints so near-term work becomes ready

B. To replace the approved contract budget

C. To calculate only the final project cost

D. To eliminate the need for a master schedule

Correct Answer: A. To remove constraints so near-term work becomes ready

Question 8

A crew installs 60 m² per labour-hour. What is its productivity for 300 m² installed in 5 labour-hours?

A. 12 m² per labour-hour

B. 60 m² per labour-hour

C. 300 m² per labour-hour

D. 1,500 m² per labour-hour

Correct Answer: B. 60 m² per labour-hour

Question 9

Which action is most consistent with lean construction?

A. Adding workers to every delayed activity regardless of workface readiness

B. Removing constraints and improving reliable flow before increasing capacity

C. Hiding small delays by changing the baseline without approval

D. Measuring progress only by elapsed calendar time

Correct Answer: B. Removing constraints and improving reliable flow before increasing capacity

Question 10

A weekly plan contains 20 commitments and 17 are completed. What is the PPC?

A. 3%

B. 17%

C. 83%

D. 85%

Correct Answer: D. 85%