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Residual

Probability and Statistics · FE Reference Handbook section

Probability and Statistics
5 formulas
10 exam-style examples
~55 min
All Probability and Statistics lectures

Handbook notes for this section

Definitions and conditions exactly as the handbook states them.

  • Confidence Interval for Intercept (â):
  • Engineering Probability and Statistics
  • Confidence Interval for Slope (b̂):
  • Sample Correlation Coefficient (R) and Coefficient of Determination (R2):

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
Residual of a regression fit — solve for residual — Residual

An engineer computes the residual between a measured and predicted strength. Given observed value (yi) = 91.4000; predicted value (yhat) = 69.6000, determine the residual (e).

Given

  • observedvalue(yi)=91.4000observed value (yi) = 91.4000
  • predictedvalue(yhat)=69.6000predicted value (yhat) = 69.6000

Find

residual (e)

Start with the thinking

  • The governing relation printed in this handbook section is Residual of a regression fit.
  • Everything except e is given, so isolate e 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.
  • The residual is the difference between an observed value and the value predicted by the regression model.

Step-by-step solution

  1. Step 1 — State the governing relation:

    ei=yi−y^ie_i = y_i - \hat{y}_i
  2. Step 2 — Rearrange symbolically for e:

    e=yi−y^ie = y_i - \hat{y}_i
  3. Step 3

    Listthegivens:observedvalue(yi)=91.4000,predictedvalue(yhat)=69.6000List the givens: observed value (yi) = 91.4000, predicted value (yhat) = 69.6000
  4. Step 4 — Substitute the given values:

    e=yi−y^ie = y_i - \hat{y}_i
  5. Step 5 — Evaluate:

    e=21.8000e = 21.8000
  6. Step 6 — Check: returning e = 21.8000 to

    ei=yi−y^ie_i = y_i - \hat{y}_i

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

Answer:
e=21.8000e = 21.8000

Why the other options are there

  • 43.6000 — kept a factor of two that cancels in the correct rearrangement.
  • 10.9000 — dropped that same factor in the other direction.
  • 23.9800 — rounded an intermediate value before the final step.

Reference: FE Handbook — Residual

Example 2
Residual of a regression fit — solve for observed value — Residual (2)

A student checks the residual of a data point on a least squares line. Given predicted value (yhat) = 64.2000; residual (e) = 4.9800, determine the observed value (yi).

Given

  • predictedvalue(yhat)=64.2000predicted value (yhat) = 64.2000
  • residual(e)=4.9800residual (e) = 4.9800

Find

observed value (yi)

Start with the thinking

  • The governing relation printed in this handbook section is Residual of a regression fit.
  • Everything except yi is given, so isolate yi 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.
  • The residual is the difference between an observed value and the value predicted by the regression model.

Step-by-step solution

  1. Step 1 — State the governing relation:

    ei=yi−y^ie_i = y_i - \hat{y}_i
  2. Step 2 — Rearrange symbolically for yi:

    yi=ei+y^iyi = e_i + \hat{y}_i
  3. Step 3

    Listthegivens:predictedvalue(yhat)=64.2000,residual(e)=4.9800List the givens: predicted value (yhat) = 64.2000, residual (e) = 4.9800
  4. Step 4 — Substitute the given values:

    yi=ei+y^iyi = e_i + \hat{y}_i
  5. Step 5 — Evaluate:

    yi=69.1800yi = 69.1800
  6. Step 6 — Check: returning yi = 69.1800 to

    ei=yi−y^ie_i = y_i - \hat{y}_i

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

Answer:
yi=69.1800yi = 69.1800

Why the other options are there

  • 138.4 — kept a factor of two that cancels in the correct rearrangement.
  • 34.5900 — dropped that same factor in the other direction.
  • 76.0980 — rounded an intermediate value before the final step.

Reference: FE Handbook — Residual

Example 3
Residual of a regression fit — solve for predicted value — Residual (3)

A large residual flags an outlier in the calibration data set. Given observed value (yi) = 94.9000; residual (e) = -7.6500, determine the predicted value (yhat).

Given

  • observedvalue(yi)=94.9000observed value (yi) = 94.9000
  • residual(e)=−7.6500residual (e) = -7.6500

Find

predicted value (yhat)

Start with the thinking

  • The governing relation printed in this handbook section is Residual of a regression fit.
  • Everything except yhat is given, so isolate yhat 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.
  • The residual is the difference between an observed value and the value predicted by the regression model.

Step-by-step solution

  1. Step 1 — State the governing relation:

    ei=yi−y^ie_i = y_i - \hat{y}_i
  2. Step 2 — Rearrange symbolically for yhat:

    yhat=yi−eiyhat = y_i - e_i
  3. Step 3

    Listthegivens:observedvalue(yi)=94.9000,residual(e)=−7.6500List the givens: observed value (yi) = 94.9000, residual (e) = -7.6500
  4. Step 4 — Substitute the given values:

    yhat=yi−eiyhat = y_i - e_i
  5. Step 5 — Evaluate:

    yhat=102.6yhat = 102.6
  6. Step 6 — Check: returning yhat = 102.6 to

    ei=yi−y^ie_i = y_i - \hat{y}_i

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

Answer:
yhat=102.6yhat = 102.6

Why the other options are there

  • 205.1 — kept a factor of two that cancels in the correct rearrangement.
  • 51.2750 — dropped that same factor in the other direction.
  • 112.8 — rounded an intermediate value before the final step.

Reference: FE Handbook — Residual

Example 4
Residual of a regression fit — solve for residual (case 2) — Residual (4)

An engineer computes the residual between a measured and predicted strength. Given observed value (yi) = 47.5000; predicted value (yhat) = 47.7000, determine the residual (e).

Given

  • observedvalue(yi)=47.5000observed value (yi) = 47.5000
  • predictedvalue(yhat)=47.7000predicted value (yhat) = 47.7000

Find

residual (e)

Start with the thinking

  • The governing relation printed in this handbook section is Residual of a regression fit.
  • Everything except e is given, so isolate e 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.
  • The residual is the difference between an observed value and the value predicted by the regression model.

Step-by-step solution

  1. Step 1 — State the governing relation:

    ei=yi−y^ie_i = y_i - \hat{y}_i
  2. Step 2 — Rearrange symbolically for e:

    e=yi−y^ie = y_i - \hat{y}_i
  3. Step 3

    Listthegivens:observedvalue(yi)=47.5000,predictedvalue(yhat)=47.7000List the givens: observed value (yi) = 47.5000, predicted value (yhat) = 47.7000
  4. Step 4 — Substitute the given values:

    e=yi−y^ie = y_i - \hat{y}_i
  5. Step 5 — Evaluate:

    e=−0.2000e = -0.2000
  6. Step 6 — Check: returning e = -0.2000 to

    ei=yi−y^ie_i = y_i - \hat{y}_i

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

Answer:
e=−0.2000e = -0.2000

Why the other options are there

  • -0.4000 — kept a factor of two that cancels in the correct rearrangement.
  • -0.1000 — dropped that same factor in the other direction.
  • -0.2200 — rounded an intermediate value before the final step.

Reference: FE Handbook — Residual

Example 5
Residual of a regression fit — solve for observed value (case 2) — Residual (5)

A student checks the residual of a data point on a least squares line. Given predicted value (yhat) = 49.6000; residual (e) = -9.1400, determine the observed value (yi).

Given

  • predictedvalue(yhat)=49.6000predicted value (yhat) = 49.6000
  • residual(e)=−9.1400residual (e) = -9.1400

Find

observed value (yi)

Start with the thinking

  • The governing relation printed in this handbook section is Residual of a regression fit.
  • Everything except yi is given, so isolate yi 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.
  • The residual is the difference between an observed value and the value predicted by the regression model.

Step-by-step solution

  1. Step 1 — State the governing relation:

    ei=yi−y^ie_i = y_i - \hat{y}_i
  2. Step 2 — Rearrange symbolically for yi:

    yi=ei+y^iyi = e_i + \hat{y}_i
  3. Step 3

    Listthegivens:predictedvalue(yhat)=49.6000,residual(e)=−9.1400List the givens: predicted value (yhat) = 49.6000, residual (e) = -9.1400
  4. Step 4 — Substitute the given values:

    yi=ei+y^iyi = e_i + \hat{y}_i
  5. Step 5 — Evaluate:

    yi=40.4600yi = 40.4600
  6. Step 6 — Check: returning yi = 40.4600 to

    ei=yi−y^ie_i = y_i - \hat{y}_i

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

Answer:
yi=40.4600yi = 40.4600

Why the other options are there

  • 80.9200 — kept a factor of two that cancels in the correct rearrangement.
  • 20.2300 — dropped that same factor in the other direction.
  • 44.5060 — rounded an intermediate value before the final step.

Reference: FE Handbook — Residual

Example 6
Residual of a regression fit — solve for predicted value (case 2) — Residual (6)

A large residual flags an outlier in the calibration data set. Given observed value (yi) = 30.0000; residual (e) = -8.0200, determine the predicted value (yhat).

Given

  • observedvalue(yi)=30.0000observed value (yi) = 30.0000
  • residual(e)=−8.0200residual (e) = -8.0200

Find

predicted value (yhat)

Start with the thinking

  • The governing relation printed in this handbook section is Residual of a regression fit.
  • Everything except yhat is given, so isolate yhat 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.
  • The residual is the difference between an observed value and the value predicted by the regression model.

Step-by-step solution

  1. Step 1 — State the governing relation:

    ei=yi−y^ie_i = y_i - \hat{y}_i
  2. Step 2 — Rearrange symbolically for yhat:

    yhat=yi−eiyhat = y_i - e_i
  3. Step 3

    Listthegivens:observedvalue(yi)=30.0000,residual(e)=−8.0200List the givens: observed value (yi) = 30.0000, residual (e) = -8.0200
  4. Step 4 — Substitute the given values:

    yhat=yi−eiyhat = y_i - e_i
  5. Step 5 — Evaluate:

    yhat=38.0200yhat = 38.0200
  6. Step 6 — Check: returning yhat = 38.0200 to

    ei=yi−y^ie_i = y_i - \hat{y}_i

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

Answer:
yhat=38.0200yhat = 38.0200

Why the other options are there

  • 76.0400 — kept a factor of two that cancels in the correct rearrangement.
  • 19.0100 — dropped that same factor in the other direction.
  • 41.8220 — rounded an intermediate value before the final step.

Reference: FE Handbook — Residual

Example 7
Residual of a regression fit — solve for residual (case 3) — Residual (7)

An engineer computes the residual between a measured and predicted strength. Given observed value (yi) = 11.1000; predicted value (yhat) = 39.9000, determine the residual (e).

Given

  • observedvalue(yi)=11.1000observed value (yi) = 11.1000
  • predictedvalue(yhat)=39.9000predicted value (yhat) = 39.9000

Find

residual (e)

Start with the thinking

  • The governing relation printed in this handbook section is Residual of a regression fit.
  • Everything except e is given, so isolate e 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.
  • The residual is the difference between an observed value and the value predicted by the regression model.

Step-by-step solution

  1. Step 1 — State the governing relation:

    ei=yi−y^ie_i = y_i - \hat{y}_i
  2. Step 2 — Rearrange symbolically for e:

    e=yi−y^ie = y_i - \hat{y}_i
  3. Step 3

    Listthegivens:observedvalue(yi)=11.1000,predictedvalue(yhat)=39.9000List the givens: observed value (yi) = 11.1000, predicted value (yhat) = 39.9000
  4. Step 4 — Substitute the given values:

    e=yi−y^ie = y_i - \hat{y}_i
  5. Step 5 — Evaluate:

    e=−28.8000e = -28.8000
  6. Step 6 — Check: returning e = -28.8000 to

    ei=yi−y^ie_i = y_i - \hat{y}_i

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

Answer:
e=−28.8000e = -28.8000

Why the other options are there

  • -57.6000 — kept a factor of two that cancels in the correct rearrangement.
  • -14.4000 — dropped that same factor in the other direction.
  • -31.6800 — rounded an intermediate value before the final step.

Reference: FE Handbook — Residual

Example 8
Residual of a regression fit — solve for observed value (case 3) — Residual (8)

A student checks the residual of a data point on a least squares line. Given predicted value (yhat) = 22.9000; residual (e) = 0.6900, determine the observed value (yi).

Given

  • predictedvalue(yhat)=22.9000predicted value (yhat) = 22.9000
  • residual(e)=0.6900residual (e) = 0.6900

Find

observed value (yi)

Start with the thinking

  • The governing relation printed in this handbook section is Residual of a regression fit.
  • Everything except yi is given, so isolate yi 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.
  • The residual is the difference between an observed value and the value predicted by the regression model.

Step-by-step solution

  1. Step 1 — State the governing relation:

    ei=yi−y^ie_i = y_i - \hat{y}_i
  2. Step 2 — Rearrange symbolically for yi:

    yi=ei+y^iyi = e_i + \hat{y}_i
  3. Step 3

    Listthegivens:predictedvalue(yhat)=22.9000,residual(e)=0.6900List the givens: predicted value (yhat) = 22.9000, residual (e) = 0.6900
  4. Step 4 — Substitute the given values:

    yi=ei+y^iyi = e_i + \hat{y}_i
  5. Step 5 — Evaluate:

    yi=23.5900yi = 23.5900
  6. Step 6 — Check: returning yi = 23.5900 to

    ei=yi−y^ie_i = y_i - \hat{y}_i

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

Answer:
yi=23.5900yi = 23.5900

Why the other options are there

  • 47.1800 — kept a factor of two that cancels in the correct rearrangement.
  • 11.7950 — dropped that same factor in the other direction.
  • 25.9490 — rounded an intermediate value before the final step.

Reference: FE Handbook — Residual

Example 9
Residual of a regression fit — solve for predicted value (case 3) — Residual (9)

A large residual flags an outlier in the calibration data set. Given observed value (yi) = 44.9000; residual (e) = -16.5500, determine the predicted value (yhat).

Given

  • observedvalue(yi)=44.9000observed value (yi) = 44.9000
  • residual(e)=−16.5500residual (e) = -16.5500

Find

predicted value (yhat)

Start with the thinking

  • The governing relation printed in this handbook section is Residual of a regression fit.
  • Everything except yhat is given, so isolate yhat 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.
  • The residual is the difference between an observed value and the value predicted by the regression model.

Step-by-step solution

  1. Step 1 — State the governing relation:

    ei=yi−y^ie_i = y_i - \hat{y}_i
  2. Step 2 — Rearrange symbolically for yhat:

    yhat=yi−eiyhat = y_i - e_i
  3. Step 3

    Listthegivens:observedvalue(yi)=44.9000,residual(e)=−16.5500List the givens: observed value (yi) = 44.9000, residual (e) = -16.5500
  4. Step 4 — Substitute the given values:

    yhat=yi−eiyhat = y_i - e_i
  5. Step 5 — Evaluate:

    yhat=61.4500yhat = 61.4500
  6. Step 6 — Check: returning yhat = 61.4500 to

    ei=yi−y^ie_i = y_i - \hat{y}_i

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

Answer:
yhat=61.4500yhat = 61.4500

Why the other options are there

  • 122.9 — kept a factor of two that cancels in the correct rearrangement.
  • 30.7250 — dropped that same factor in the other direction.
  • 67.5950 — rounded an intermediate value before the final step.

Reference: FE Handbook — Residual

Example 10
Residual of a regression fit — solve for residual (case 4) — Residual (10)

An engineer computes the residual between a measured and predicted strength. Given observed value (yi) = 96.0000; predicted value (yhat) = 32.5000, determine the residual (e).

Given

  • observedvalue(yi)=96.0000observed value (yi) = 96.0000
  • predictedvalue(yhat)=32.5000predicted value (yhat) = 32.5000

Find

residual (e)

Start with the thinking

  • The governing relation printed in this handbook section is Residual of a regression fit.
  • Everything except e is given, so isolate e 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.
  • The residual is the difference between an observed value and the value predicted by the regression model.

Step-by-step solution

  1. Step 1 — State the governing relation:

    ei=yi−y^ie_i = y_i - \hat{y}_i
  2. Step 2 — Rearrange symbolically for e:

    e=yi−y^ie = y_i - \hat{y}_i
  3. Step 3

    Listthegivens:observedvalue(yi)=96.0000,predictedvalue(yhat)=32.5000List the givens: observed value (yi) = 96.0000, predicted value (yhat) = 32.5000
  4. Step 4 — Substitute the given values:

    e=yi−y^ie = y_i - \hat{y}_i
  5. Step 5 — Evaluate:

    e=63.5000e = 63.5000
  6. Step 6 — Check: returning e = 63.5000 to

    ei=yi−y^ie_i = y_i - \hat{y}_i

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

Answer:
e=63.5000e = 63.5000

Why the other options are there

  • 127.0 — kept a factor of two that cancels in the correct rearrangement.
  • 31.7500 — dropped that same factor in the other direction.
  • 69.8500 — rounded an intermediate value before the final step.

Reference: FE Handbook — Residual

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