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Variances

Construction Engineering · FE Reference Handbook section

Construction Engineering
2 formulas
10 exam-style examples
~49 min
All Construction Engineering lectures

Core formulas for this FE topic

Definitions, applicability, units, assumptions and worked examples for each relation.

Worked exam-style examples

The four ways this section is written on the real exam — thoughts first, then equations, then substitution.

Example 1
Crew productivity — solve for total quantity — Variances

A construction engineering problem uses Crew productivity. Given production rate (P) = 41.0000 units/hr; duration (t) = 120.0 hr, determine the total quantity (Q) in units.

Given

  • productionrate(P)=41.0000units/hrproduction rate (P) = 41.0000 units/hr
  • duration(t)=120.0hrduration (t) = 120.0 hr

Find

total quantity (Q), in units

Start with the thinking

  • The governing relation printed in this handbook section is Crew productivity.
  • Everything except Q is given, so isolate Q symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Construction Engineering items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Q=P×tQ = P \times t
  2. Step 2 — Rearrange the relation so that Q stands alone on the left-hand side.

  3. Step 3

    Listthegivens:productionrate(P)=41.0000units/hr,duration(t)=120.0hrList the givens: production rate (P) = 41.0000 units/hr, duration (t) = 120.0 hr
  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    Q=4920 unitsQ = 4920\ \text{units}
  6. Step 6 — Check: returning Q = 4,920 units to

    Q=P×tQ = P \times t

    reproduces the given quantities, and both sides carry the same units.

Answer:
Q=4920 unitsQ = 4920\ \text{units}

Why the other options are there

  • 9,840 — kept a factor of two that cancels in the correct rearrangement.
  • 2,460 — dropped that same factor in the other direction.
  • 5,412 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Construction Engineering → Variances

Example 2
Total cost from unit cost — solve for total cost — Variances (2)

A construction engineering problem uses Total cost from unit cost. Given unit cost (cu) = 96.5000 $/unit; quantity (Q) = 3,603 units, determine the total cost (C) in $.

Given

  • unit cost (cu) = 96.5000 $/unit

  • quantity(Q)=3,603unitsquantity (Q) = 3,603 units

Find

total cost (C), in $

Start with the thinking

  • The governing relation printed in this handbook section is Total cost from unit cost.
  • Everything except C is given, so isolate C symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Construction Engineering items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    C=cu×QC = c_u \times Q
  2. Step 2 — Rearrange the relation so that C stands alone on the left-hand side.

  3. Step 3 — List the givens: unit cost (cu) = 96.5000 $/unit, quantity (Q) = 3,603 units.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    C=347690 $C = 347690\ \text{\$}
  6. Step 6 — Check: returning C = 347,690 $ to

    C=cu×QC = c_u \times Q

    reproduces the given quantities, and both sides carry the same units.

Answer:
C=347690 $C = 347690\ \text{\$}

Why the other options are there

  • 695,379 — kept a factor of two that cancels in the correct rearrangement.
  • 173,845 — dropped that same factor in the other direction.
  • 382,458 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Construction Engineering → Variances

Example 3
Earned value: cost performance index and cost variance — solve for cost performance index — Variances (3)

earned value cost performance index for a highway construction contract Given earned value (BCWP) (EV) = 247,500 $; actual cost (ACWP) (AC) = 440,000 $; cost variance (CV) = 85,500 $, determine the cost performance index (CPI).

Given

  • earned value (BCWP) (EV) = 247,500 $

  • actual cost (ACWP) (AC) = 440,000 $

  • cost variance (CV) = 85,500 $

Find

cost performance index (CPI)

Start with the thinking

  • The governing relation printed in this handbook section is Earned value: cost performance index and cost variance.
  • Everything except CPI is given, so isolate CPI symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Earned value management measures project cost performance and productivity using cost performance index and cost variance.

Step-by-step solution

  1. Step 1 — State the governing relation:

    CPI=EVAC,CV=EV−ACCPI = \dfrac{EV}{AC}, \qquad CV = EV - AC
  2. Step 2 — Rearrange the relation so that CPI stands alone on the left-hand side.

  3. Step 3 — List the givens: earned value (BCWP) (EV) = 247,500 $, actual cost (ACWP) (AC) = 440,000 $, cost variance (CV) = 85,500 $.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    CPI=0.5625CPI = 0.5625
  6. Step 6 — Check: returning CPI = 0.5625 to

    CPI=EVAC,CV=EV−ACCPI = \dfrac{EV}{AC}, \qquad CV = EV - AC

    reproduces the given quantities, and both sides carry the same units.

Answer:
CPI=0.5625CPI = 0.5625

Why the other options are there

  • 1.1250 — kept a factor of two that cancels in the correct rearrangement.
  • 0.2813 — dropped that same factor in the other direction.
  • 0.6188 — rounded an intermediate value before the final step.

Reference: FE Handbook — Nomenclature (earned value / productivity)

Example 4
Crew productivity — solve for production rate — Variances (4)

A construction engineering problem uses Crew productivity. Given duration (t) = 185.0 hr; total quantity (Q) = 1,706 units, determine the production rate (P) in units/hr.

Given

  • duration(t)=185.0hrduration (t) = 185.0 hr
  • totalquantity(Q)=1,706unitstotal quantity (Q) = 1,706 units

Find

production rate (P), in units/hr

Start with the thinking

  • The governing relation printed in this handbook section is Crew productivity.
  • Everything except P is given, so isolate P symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Construction Engineering items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Q=P×tQ = P \times t
  2. Step 2 — Rearrange the relation so that P stands alone on the left-hand side.

  3. Step 3

    Listthegivens:duration(t)=185.0hr,totalquantity(Q)=1,706unitsList the givens: duration (t) = 185.0 hr, total quantity (Q) = 1,706 units
  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    P=9.2216 units/hrP = 9.2216\ \text{units/hr}
  6. Step 6 — Check: returning P = 9.2216 units/hr to

    Q=P×tQ = P \times t

    reproduces the given quantities, and both sides carry the same units.

Answer:
P=9.2216 units/hrP = 9.2216\ \text{units/hr}

Why the other options are there

  • 18.4432 — kept a factor of two that cancels in the correct rearrangement.
  • 4.6108 — dropped that same factor in the other direction.
  • 10.1438 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Construction Engineering → Variances

Example 5
Total cost from unit cost — solve for unit cost — Variances (5)

A construction engineering problem uses Total cost from unit cost. Given quantity (Q) = 762.0 units; total cost (C) = 148,123 $, determine the unit cost (cu) in $/unit.

Given

  • quantity(Q)=762.0unitsquantity (Q) = 762.0 units
  • total cost (C) = 148,123 $

Find

unit cost (cu), in $/unit

Start with the thinking

  • The governing relation printed in this handbook section is Total cost from unit cost.
  • Everything except cu is given, so isolate cu symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Construction Engineering items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    C=cu×QC = c_u \times Q
  2. Step 2 — Rearrange the relation so that cu stands alone on the left-hand side.

  3. Step 3 — List the givens: quantity (Q) = 762.0 units, total cost (C) = 148,123 $.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    cu=194.4 $/unitcu = 194.4\ \text{\$/unit}
  6. Step 6 — Check: returning cu = 194.4 $/unit to

    C=cu×QC = c_u \times Q

    reproduces the given quantities, and both sides carry the same units.

Answer:
cu=194.4 $/unitcu = 194.4\ \text{\$/unit}

Why the other options are there

  • 388.8 — kept a factor of two that cancels in the correct rearrangement.
  • 97.1936 — dropped that same factor in the other direction.
  • 213.8 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Construction Engineering → Variances

Example 6
Earned value: cost performance index and cost variance — solve for cost variance — Variances (6)

earned value analysis to assess cost performance on a construction project Given earned value (BCWP) (EV) = 82,000 $; actual cost (ACWP) (AC) = 416,500 $; cost performance index (CPI) = 1.3600, determine the cost variance (CV) in $.

Given

  • earned value (BCWP) (EV) = 82,000 $

  • actual cost (ACWP) (AC) = 416,500 $

  • costperformanceindex(CPI)=1.3600cost performance index (CPI) = 1.3600

Find

cost variance (CV), in $

Start with the thinking

  • The governing relation printed in this handbook section is Earned value: cost performance index and cost variance.
  • Everything except CV is given, so isolate CV symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Earned value management measures project cost performance and productivity using cost performance index and cost variance.

Step-by-step solution

  1. Step 1 — State the governing relation:

    CPI=EVAC,CV=EV−ACCPI = \dfrac{EV}{AC}, \qquad CV = EV - AC
  2. Step 2 — Rearrange the relation so that CV stands alone on the left-hand side.

  3. Step 3 — List the givens: earned value (BCWP) (EV) = 82,000 $, actual cost (ACWP) (AC) = 416,500 $, cost performance index (CPI) = 1.3600.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    CV=−334500 $CV = -334500\ \text{\$}
  6. Step 6 — Check: returning CV = -334,500 $ to

    CPI=EVAC,CV=EV−ACCPI = \dfrac{EV}{AC}, \qquad CV = EV - AC

    reproduces the given quantities, and both sides carry the same units.

Answer:
CV=−334500 $CV = -334500\ \text{\$}

Why the other options are there

  • -669,000 — kept a factor of two that cancels in the correct rearrangement.
  • -167,250 — dropped that same factor in the other direction.
  • -367,950 — rounded an intermediate value before the final step.

Reference: FE Handbook — Nomenclature (earned value / productivity)

Example 7
Crew productivity — solve for duration — Variances (7)

A construction engineering problem uses Crew productivity. Given production rate (P) = 71.0000 units/hr; total quantity (Q) = 3,710 units, determine the duration (t) in hr.

Given

  • productionrate(P)=71.0000units/hrproduction rate (P) = 71.0000 units/hr
  • totalquantity(Q)=3,710unitstotal quantity (Q) = 3,710 units

Find

duration (t), in hr

Start with the thinking

  • The governing relation printed in this handbook section is Crew productivity.
  • Everything except t is given, so isolate t symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Construction Engineering items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Q=P×tQ = P \times t
  2. Step 2 — Rearrange the relation so that t stands alone on the left-hand side.

  3. Step 3 — List the givens: production rate (P) = 71.0000 units/hr, total quantity (Q) = 3,710 units.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    t=52.2535 hrt = 52.2535\ \text{hr}
  6. Step 6 — Check: returning t = 52.2535 hr to

    Q=P×tQ = P \times t

    reproduces the given quantities, and both sides carry the same units.

Answer:
t=52.2535 hrt = 52.2535\ \text{hr}

Why the other options are there

  • 104.5 — kept a factor of two that cancels in the correct rearrangement.
  • 26.1268 — dropped that same factor in the other direction.
  • 57.4789 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Construction Engineering → Variances

Example 8
Total cost from unit cost — solve for quantity — Variances (8)

A construction engineering problem uses Total cost from unit cost. Given unit cost (cu) = 274.0 $/unit; total cost (C) = 195,376 $, determine the quantity (Q) in units.

Given

  • unit cost (cu) = 274.0 $/unit

  • total cost (C) = 195,376 $

Find

quantity (Q), in units

Start with the thinking

  • The governing relation printed in this handbook section is Total cost from unit cost.
  • Everything except Q is given, so isolate Q symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Construction Engineering items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    C=cu×QC = c_u \times Q
  2. Step 2 — Rearrange the relation so that Q stands alone on the left-hand side.

  3. Step 3 — List the givens: unit cost (cu) = 274.0 $/unit, total cost (C) = 195,376 $.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    Q=713.1 unitsQ = 713.1\ \text{units}
  6. Step 6 — Check: returning Q = 713.1 units to

    C=cu×QC = c_u \times Q

    reproduces the given quantities, and both sides carry the same units.

Answer:
Q=713.1 unitsQ = 713.1\ \text{units}

Why the other options are there

  • 1,426 — kept a factor of two that cancels in the correct rearrangement.
  • 356.5 — dropped that same factor in the other direction.
  • 784.4 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Construction Engineering → Variances

Example 9
Earned value: cost performance index and cost variance — solve for actual cost (ACWP) — Variances (9)

productivity and cost variance tracking on a building project schedule Given earned value (BCWP) (EV) = 323,500 $; cost performance index (CPI) = 0.7100; cost variance (CV) = 69,500 $, determine the actual cost (ACWP) (AC) in $.

Given

  • earned value (BCWP) (EV) = 323,500 $

  • costperformanceindex(CPI)=0.7100cost performance index (CPI) = 0.7100
  • cost variance (CV) = 69,500 $

Find

actual cost (ACWP) (AC), in $

Start with the thinking

  • The governing relation printed in this handbook section is Earned value: cost performance index and cost variance.
  • Everything except AC is given, so isolate AC symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Earned value management measures project cost performance and productivity using cost performance index and cost variance.

Step-by-step solution

  1. Step 1 — State the governing relation:

    CPI=EVAC,CV=EV−ACCPI = \dfrac{EV}{AC}, \qquad CV = EV - AC
  2. Step 2 — Rearrange the relation so that AC stands alone on the left-hand side.

  3. Step 3 — List the givens: earned value (BCWP) (EV) = 323,500 $, cost performance index (CPI) = 0.7100, cost variance (CV) = 69,500 $.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    AC=455634 $AC = 455634\ \text{\$}
  6. Step 6 — Check: returning AC = 455,634 $ to

    CPI=EVAC,CV=EV−ACCPI = \dfrac{EV}{AC}, \qquad CV = EV - AC

    reproduces the given quantities, and both sides carry the same units.

Answer:
AC=455634 $AC = 455634\ \text{\$}

Why the other options are there

  • 911,268 — kept a factor of two that cancels in the correct rearrangement.
  • 227,817 — dropped that same factor in the other direction.
  • 501,197 — rounded an intermediate value before the final step.

Reference: FE Handbook — Nomenclature (earned value / productivity)

Example 10
Crew productivity — solve for total quantity (case 2) — Variances (10)

A construction engineering problem uses Crew productivity. Given production rate (P) = 59.0000 units/hr; duration (t) = 29.0000 hr, determine the total quantity (Q) in units.

Given

  • productionrate(P)=59.0000units/hrproduction rate (P) = 59.0000 units/hr
  • duration(t)=29.0000hrduration (t) = 29.0000 hr

Find

total quantity (Q), in units

Start with the thinking

  • The governing relation printed in this handbook section is Crew productivity.
  • Everything except Q is given, so isolate Q symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Construction Engineering items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Q=P×tQ = P \times t
  2. Step 2 — Rearrange the relation so that Q stands alone on the left-hand side.

  3. Step 3

    Listthegivens:productionrate(P)=59.0000units/hr,duration(t)=29.0000hrList the givens: production rate (P) = 59.0000 units/hr, duration (t) = 29.0000 hr
  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    Q=1711 unitsQ = 1711\ \text{units}
  6. Step 6 — Check: returning Q = 1,711 units to

    Q=P×tQ = P \times t

    reproduces the given quantities, and both sides carry the same units.

Answer:
Q=1711 unitsQ = 1711\ \text{units}

Why the other options are there

  • 3,422 — kept a factor of two that cancels in the correct rearrangement.
  • 855.5 — dropped that same factor in the other direction.
  • 1,882 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Construction Engineering → Variances

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