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Test Statistics

Probability and Statistics · FE Reference Handbook section

Probability and Statistics
12 formulas
10 exam-style examples
~60 min
All Probability and Statistics lectures

Handbook notes for this section

Definitions and conditions exactly as the handbook states them.

  • The Z score is applicable when the standard deviation (s) is known. The test statistic is applicable when the standard deviation
  • Engineering Probability and Statistics

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
Test statistic — Student's t — solve for test statistic — Test Statistics

An engineer computes a test statistic to compare a small sample mean to a target value. Given sample mean (xbar) = 98.9000; hypothesized mean (mu0) = 91.7000; sample std dev (s) = 3.4000; sample size (n) = 22.0000, determine the test statistic (t).

Given

  • samplemean(xbar)=98.9000sample mean (xbar) = 98.9000
  • hypothesizedmean(mu0)=91.7000hypothesized mean (mu_{0}) = 91.7000
  • samplestddev(s)=3.4000sample std dev (s) = 3.4000
  • samplesize(n)=22.0000sample size (n) = 22.0000

Find

test statistic (t)

Start with the thinking

  • The governing relation printed in this handbook section is Test statistic — Student's t.
  • 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.
  • This test statistic follows Student's t distribution for small-sample hypothesis testing.

Step-by-step solution

  1. Step 1 — State the governing relation:

    t=xˉ−μ0s/nt = \dfrac{\bar{x}-\mu_0}{s/\sqrt{n}}
  2. Step 2 — Rearrange symbolically for t:

    t=xˉ−μ0s/nt = \dfrac{\bar{x}-\mu_0}{s/\sqrt{n}}
  3. Step 3 — List the givens: sample mean (xbar) = 98.9000, hypothesized mean (mu0) = 91.7000, sample std dev (s) = 3.4000, sample size (n) = 22.0000.

  4. Step 4 — Substitute the given values:

    t=xˉ−μ03.4000/22.0000t = \dfrac{\bar{x}-\mu_0}{3.4000/\sqrt{22.0000}}
  5. Step 5 — Evaluate:

    t=9.9326t = 9.9326
  6. Step 6 — Check: returning t = 9.9326 to

    t=xˉ−μ0s/nt = \dfrac{\bar{x}-\mu_0}{s/\sqrt{n}}

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

Answer:
t=9.9326t = 9.9326

Why the other options are there

  • 19.8653 — kept a factor of two that cancels in the correct rearrangement.
  • 4.9663 — dropped that same factor in the other direction.
  • 10.9259 — rounded an intermediate value before the final step.

Reference: FE Handbook — Test Statistics

Example 2
Test statistic — Student's t — solve for sample mean — Test Statistics (2)

A student calculates the t test statistic for a lab measurement series. Given hypothesized mean (mu0) = 92.5000; sample std dev (s) = 3.3000; sample size (n) = 11.0000; test statistic (t) = 6.3900, determine the sample mean (xbar).

Given

  • hypothesizedmean(mu0)=92.5000hypothesized mean (mu_{0}) = 92.5000
  • samplestddev(s)=3.3000sample std dev (s) = 3.3000
  • samplesize(n)=11.0000sample size (n) = 11.0000
  • teststatistic(t)=6.3900test statistic (t) = 6.3900

Find

sample mean (xbar)

Start with the thinking

  • The governing relation printed in this handbook section is Test statistic — Student's t.
  • Everything except xbar is given, so isolate xbar 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.
  • This test statistic follows Student's t distribution for small-sample hypothesis testing.

Step-by-step solution

  1. Step 1 — State the governing relation:

    t=xˉ−μ0s/nt = \dfrac{\bar{x}-\mu_0}{s/\sqrt{n}}
  2. Step 2 — Rearrange symbolically for xbar:

    xbar=μ0+tsnxbar = \mu_0 + t\dfrac{s}{\sqrt{n}}
  3. Step 3 — List the givens: hypothesized mean (mu0) = 92.5000, sample std dev (s) = 3.3000, sample size (n) = 11.0000, test statistic (t) = 6.3900.

  4. Step 4 — Substitute the given values:

    xbar=μ0+6.39003.300011.0000xbar = \mu_0 + 6.3900\dfrac{3.3000}{\sqrt{11.0000}}
  5. Step 5 — Evaluate:

    xbar=98.8580xbar = 98.8580
  6. Step 6 — Check: returning xbar = 98.8580 to

    t=xˉ−μ0s/nt = \dfrac{\bar{x}-\mu_0}{s/\sqrt{n}}

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

Answer:
xbar=98.8580xbar = 98.8580

Why the other options are there

  • 197.7 — kept a factor of two that cancels in the correct rearrangement.
  • 49.4290 — dropped that same factor in the other direction.
  • 108.7 — rounded an intermediate value before the final step.

Reference: FE Handbook — Test Statistics

Example 3
Test statistic — Student's t — solve for sample std dev — Test Statistics (3)

The test statistic exceeds the critical value, leading to rejection of the null hypothesis. Given sample mean (xbar) = 104.8; hypothesized mean (mu0) = 98.1000; sample size (n) = 23.0000; test statistic (t) = 5.0500, determine the sample std dev (s).

Given

  • samplemean(xbar)=104.8sample mean (xbar) = 104.8
  • hypothesizedmean(mu0)=98.1000hypothesized mean (mu_{0}) = 98.1000
  • samplesize(n)=23.0000sample size (n) = 23.0000
  • teststatistic(t)=5.0500test statistic (t) = 5.0500

Find

sample std dev (s)

Start with the thinking

  • The governing relation printed in this handbook section is Test statistic — Student's t.
  • Everything except s is given, so isolate s 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.
  • This test statistic follows Student's t distribution for small-sample hypothesis testing.

Step-by-step solution

  1. Step 1 — State the governing relation:

    t=xˉ−μ0s/nt = \dfrac{\bar{x}-\mu_0}{s/\sqrt{n}}
  2. Step 2 — Rearrange symbolically for s:

    s=(xˉ−μ0)nts = \dfrac{(\bar{x}-\mu_0)\sqrt{n}}{t}
  3. Step 3 — List the givens: sample mean (xbar) = 104.8, hypothesized mean (mu0) = 98.1000, sample size (n) = 23.0000, test statistic (t) = 5.0500.

  4. Step 4 — Substitute the given values:

    s=(xˉ−μ0)23.00005.0500s = \dfrac{(\bar{x}-\mu_0)\sqrt{23.0000}}{5.0500}
  5. Step 5 — Evaluate:

    s=6.3628s = 6.3628
  6. Step 6 — Check: returning s = 6.3628 to

    t=xˉ−μ0s/nt = \dfrac{\bar{x}-\mu_0}{s/\sqrt{n}}

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

Answer:
s=6.3628s = 6.3628

Why the other options are there

  • 12.7256 — kept a factor of two that cancels in the correct rearrangement.
  • 3.1814 — dropped that same factor in the other direction.
  • 6.9991 — rounded an intermediate value before the final step.

Reference: FE Handbook — Test Statistics

Example 4
Test statistic — Student's t — solve for test statistic (case 2) — Test Statistics (4)

An engineer computes a test statistic to compare a small sample mean to a target value. Given sample mean (xbar) = 107.0; hypothesized mean (mu0) = 95.2000; sample std dev (s) = 2.1000; sample size (n) = 6.0000, determine the test statistic (t).

Given

  • samplemean(xbar)=107.0sample mean (xbar) = 107.0
  • hypothesizedmean(mu0)=95.2000hypothesized mean (mu_{0}) = 95.2000
  • samplestddev(s)=2.1000sample std dev (s) = 2.1000
  • samplesize(n)=6.0000sample size (n) = 6.0000

Find

test statistic (t)

Start with the thinking

  • The governing relation printed in this handbook section is Test statistic — Student's t.
  • 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.
  • This test statistic follows Student's t distribution for small-sample hypothesis testing.

Step-by-step solution

  1. Step 1 — State the governing relation:

    t=xˉ−μ0s/nt = \dfrac{\bar{x}-\mu_0}{s/\sqrt{n}}
  2. Step 2 — Rearrange symbolically for t:

    t=xˉ−μ0s/nt = \dfrac{\bar{x}-\mu_0}{s/\sqrt{n}}
  3. Step 3 — List the givens: sample mean (xbar) = 107.0, hypothesized mean (mu0) = 95.2000, sample std dev (s) = 2.1000, sample size (n) = 6.0000.

  4. Step 4 — Substitute the given values:

    t=xˉ−μ02.1000/6.0000t = \dfrac{\bar{x}-\mu_0}{2.1000/\sqrt{6.0000}}
  5. Step 5 — Evaluate:

    t=13.7638t = 13.7638
  6. Step 6 — Check: returning t = 13.7638 to

    t=xˉ−μ0s/nt = \dfrac{\bar{x}-\mu_0}{s/\sqrt{n}}

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

Answer:
t=13.7638t = 13.7638

Why the other options are there

  • 27.5276 — kept a factor of two that cancels in the correct rearrangement.
  • 6.8819 — dropped that same factor in the other direction.
  • 15.1402 — rounded an intermediate value before the final step.

Reference: FE Handbook — Test Statistics

Example 5
Test statistic — Student's t — solve for sample mean (case 2) — Test Statistics (5)

A student calculates the t test statistic for a lab measurement series. Given hypothesized mean (mu0) = 95.8000; sample std dev (s) = 8.5000; sample size (n) = 19.0000; test statistic (t) = 3.6900, determine the sample mean (xbar).

Given

  • hypothesizedmean(mu0)=95.8000hypothesized mean (mu_{0}) = 95.8000
  • samplestddev(s)=8.5000sample std dev (s) = 8.5000
  • samplesize(n)=19.0000sample size (n) = 19.0000
  • teststatistic(t)=3.6900test statistic (t) = 3.6900

Find

sample mean (xbar)

Start with the thinking

  • The governing relation printed in this handbook section is Test statistic — Student's t.
  • Everything except xbar is given, so isolate xbar 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.
  • This test statistic follows Student's t distribution for small-sample hypothesis testing.

Step-by-step solution

  1. Step 1 — State the governing relation:

    t=xˉ−μ0s/nt = \dfrac{\bar{x}-\mu_0}{s/\sqrt{n}}
  2. Step 2 — Rearrange symbolically for xbar:

    xbar=μ0+tsnxbar = \mu_0 + t\dfrac{s}{\sqrt{n}}
  3. Step 3 — List the givens: hypothesized mean (mu0) = 95.8000, sample std dev (s) = 8.5000, sample size (n) = 19.0000, test statistic (t) = 3.6900.

  4. Step 4 — Substitute the given values:

    xbar=μ0+3.69008.500019.0000xbar = \mu_0 + 3.6900\dfrac{8.5000}{\sqrt{19.0000}}
  5. Step 5 — Evaluate:

    xbar=103.0xbar = 103.0
  6. Step 6 — Check: returning xbar = 103.0 to

    t=xˉ−μ0s/nt = \dfrac{\bar{x}-\mu_0}{s/\sqrt{n}}

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

Answer:
xbar=103.0xbar = 103.0

Why the other options are there

  • 206.0 — kept a factor of two that cancels in the correct rearrangement.
  • 51.4978 — dropped that same factor in the other direction.
  • 113.3 — rounded an intermediate value before the final step.

Reference: FE Handbook — Test Statistics

Example 6
Test statistic — Student's t — solve for sample std dev (case 2) — Test Statistics (6)

The test statistic exceeds the critical value, leading to rejection of the null hypothesis. Given sample mean (xbar) = 98.5000; hypothesized mean (mu0) = 96.2000; sample size (n) = 30.0000; test statistic (t) = 4.2100, determine the sample std dev (s).

Given

  • samplemean(xbar)=98.5000sample mean (xbar) = 98.5000
  • hypothesizedmean(mu0)=96.2000hypothesized mean (mu_{0}) = 96.2000
  • samplesize(n)=30.0000sample size (n) = 30.0000
  • teststatistic(t)=4.2100test statistic (t) = 4.2100

Find

sample std dev (s)

Start with the thinking

  • The governing relation printed in this handbook section is Test statistic — Student's t.
  • Everything except s is given, so isolate s 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.
  • This test statistic follows Student's t distribution for small-sample hypothesis testing.

Step-by-step solution

  1. Step 1 — State the governing relation:

    t=xˉ−μ0s/nt = \dfrac{\bar{x}-\mu_0}{s/\sqrt{n}}
  2. Step 2 — Rearrange symbolically for s:

    s=(xˉ−μ0)nts = \dfrac{(\bar{x}-\mu_0)\sqrt{n}}{t}
  3. Step 3 — List the givens: sample mean (xbar) = 98.5000, hypothesized mean (mu0) = 96.2000, sample size (n) = 30.0000, test statistic (t) = 4.2100.

  4. Step 4 — Substitute the given values:

    s=(xˉ−μ0)30.00004.2100s = \dfrac{(\bar{x}-\mu_0)\sqrt{30.0000}}{4.2100}
  5. Step 5 — Evaluate:

    s=2.9923s = 2.9923
  6. Step 6 — Check: returning s = 2.9923 to

    t=xˉ−μ0s/nt = \dfrac{\bar{x}-\mu_0}{s/\sqrt{n}}

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

Answer:
s=2.9923s = 2.9923

Why the other options are there

  • 5.9846 — kept a factor of two that cancels in the correct rearrangement.
  • 1.4962 — dropped that same factor in the other direction.
  • 3.2915 — rounded an intermediate value before the final step.

Reference: FE Handbook — Test Statistics

Example 7
Test statistic — Student's t — solve for test statistic (case 3) — Test Statistics (7)

An engineer computes a test statistic to compare a small sample mean to a target value. Given sample mean (xbar) = 104.9; hypothesized mean (mu0) = 95.4000; sample std dev (s) = 7.3000; sample size (n) = 27.0000, determine the test statistic (t).

Given

  • samplemean(xbar)=104.9sample mean (xbar) = 104.9
  • hypothesizedmean(mu0)=95.4000hypothesized mean (mu_{0}) = 95.4000
  • samplestddev(s)=7.3000sample std dev (s) = 7.3000
  • samplesize(n)=27.0000sample size (n) = 27.0000

Find

test statistic (t)

Start with the thinking

  • The governing relation printed in this handbook section is Test statistic — Student's t.
  • 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.
  • This test statistic follows Student's t distribution for small-sample hypothesis testing.

Step-by-step solution

  1. Step 1 — State the governing relation:

    t=xˉ−μ0s/nt = \dfrac{\bar{x}-\mu_0}{s/\sqrt{n}}
  2. Step 2 — Rearrange symbolically for t:

    t=xˉ−μ0s/nt = \dfrac{\bar{x}-\mu_0}{s/\sqrt{n}}
  3. Step 3 — List the givens: sample mean (xbar) = 104.9, hypothesized mean (mu0) = 95.4000, sample std dev (s) = 7.3000, sample size (n) = 27.0000.

  4. Step 4 — Substitute the given values:

    t=xˉ−μ07.3000/27.0000t = \dfrac{\bar{x}-\mu_0}{7.3000/\sqrt{27.0000}}
  5. Step 5 — Evaluate:

    t=6.7621t = 6.7621
  6. Step 6 — Check: returning t = 6.7621 to

    t=xˉ−μ0s/nt = \dfrac{\bar{x}-\mu_0}{s/\sqrt{n}}

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

Answer:
t=6.7621t = 6.7621

Why the other options are there

  • 13.5242 — kept a factor of two that cancels in the correct rearrangement.
  • 3.3811 — dropped that same factor in the other direction.
  • 7.4383 — rounded an intermediate value before the final step.

Reference: FE Handbook — Test Statistics

Example 8
Test statistic — Student's t — solve for sample mean (case 3) — Test Statistics (8)

A student calculates the t test statistic for a lab measurement series. Given hypothesized mean (mu0) = 99.4000; sample std dev (s) = 3.1000; sample size (n) = 20.0000; test statistic (t) = -3.1900, determine the sample mean (xbar).

Given

  • hypothesizedmean(mu0)=99.4000hypothesized mean (mu_{0}) = 99.4000
  • samplestddev(s)=3.1000sample std dev (s) = 3.1000
  • samplesize(n)=20.0000sample size (n) = 20.0000
  • teststatistic(t)=−3.1900test statistic (t) = -3.1900

Find

sample mean (xbar)

Start with the thinking

  • The governing relation printed in this handbook section is Test statistic — Student's t.
  • Everything except xbar is given, so isolate xbar 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.
  • This test statistic follows Student's t distribution for small-sample hypothesis testing.

Step-by-step solution

  1. Step 1 — State the governing relation:

    t=xˉ−μ0s/nt = \dfrac{\bar{x}-\mu_0}{s/\sqrt{n}}
  2. Step 2 — Rearrange symbolically for xbar:

    xbar=μ0+tsnxbar = \mu_0 + t\dfrac{s}{\sqrt{n}}
  3. Step 3 — List the givens: hypothesized mean (mu0) = 99.4000, sample std dev (s) = 3.1000, sample size (n) = 20.0000, test statistic (t) = -3.1900.

  4. Step 4 — Substitute the given values:

    xbar=μ0+−3.19003.100020.0000xbar = \mu_0 + -3.1900\dfrac{3.1000}{\sqrt{20.0000}}
  5. Step 5 — Evaluate:

    xbar=97.1888xbar = 97.1888
  6. Step 6 — Check: returning xbar = 97.1888 to

    t=xˉ−μ0s/nt = \dfrac{\bar{x}-\mu_0}{s/\sqrt{n}}

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

Answer:
xbar=97.1888xbar = 97.1888

Why the other options are there

  • 194.4 — kept a factor of two that cancels in the correct rearrangement.
  • 48.5944 — dropped that same factor in the other direction.
  • 106.9 — rounded an intermediate value before the final step.

Reference: FE Handbook — Test Statistics

Example 9
Test statistic — Student's t — solve for sample std dev (case 3) — Test Statistics (9)

The test statistic exceeds the critical value, leading to rejection of the null hypothesis. Given sample mean (xbar) = 96.0000; hypothesized mean (mu0) = 94.6000; sample size (n) = 17.0000; test statistic (t) = -3.0800, determine the sample std dev (s).

Given

  • samplemean(xbar)=96.0000sample mean (xbar) = 96.0000
  • hypothesizedmean(mu0)=94.6000hypothesized mean (mu_{0}) = 94.6000
  • samplesize(n)=17.0000sample size (n) = 17.0000
  • teststatistic(t)=−3.0800test statistic (t) = -3.0800

Find

sample std dev (s)

Start with the thinking

  • The governing relation printed in this handbook section is Test statistic — Student's t.
  • Everything except s is given, so isolate s 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.
  • This test statistic follows Student's t distribution for small-sample hypothesis testing.

Step-by-step solution

  1. Step 1 — State the governing relation:

    t=xˉ−μ0s/nt = \dfrac{\bar{x}-\mu_0}{s/\sqrt{n}}
  2. Step 2 — Rearrange symbolically for s:

    s=(xˉ−μ0)nts = \dfrac{(\bar{x}-\mu_0)\sqrt{n}}{t}
  3. Step 3 — List the givens: sample mean (xbar) = 96.0000, hypothesized mean (mu0) = 94.6000, sample size (n) = 17.0000, test statistic (t) = -3.0800.

  4. Step 4 — Substitute the given values:

    s=(xˉ−μ0)17.0000−3.0800s = \dfrac{(\bar{x}-\mu_0)\sqrt{17.0000}}{-3.0800}
  5. Step 5 — Evaluate:

    s=−1.8741s = -1.8741
  6. Step 6 — Check: returning s = -1.8741 to

    t=xˉ−μ0s/nt = \dfrac{\bar{x}-\mu_0}{s/\sqrt{n}}

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

Answer:
s=−1.8741s = -1.8741

Why the other options are there

  • -3.7483 — kept a factor of two that cancels in the correct rearrangement.
  • -0.9371 — dropped that same factor in the other direction.
  • -2.0616 — rounded an intermediate value before the final step.

Reference: FE Handbook — Test Statistics

Example 10
Test statistic — Student's t — solve for test statistic (case 4) — Test Statistics (10)

An engineer computes a test statistic to compare a small sample mean to a target value. Given sample mean (xbar) = 96.1000; hypothesized mean (mu0) = 96.4000; sample std dev (s) = 2.3000; sample size (n) = 26.0000, determine the test statistic (t).

Given

  • samplemean(xbar)=96.1000sample mean (xbar) = 96.1000
  • hypothesizedmean(mu0)=96.4000hypothesized mean (mu_{0}) = 96.4000
  • samplestddev(s)=2.3000sample std dev (s) = 2.3000
  • samplesize(n)=26.0000sample size (n) = 26.0000

Find

test statistic (t)

Start with the thinking

  • The governing relation printed in this handbook section is Test statistic — Student's t.
  • 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.
  • This test statistic follows Student's t distribution for small-sample hypothesis testing.

Step-by-step solution

  1. Step 1 — State the governing relation:

    t=xˉ−μ0s/nt = \dfrac{\bar{x}-\mu_0}{s/\sqrt{n}}
  2. Step 2 — Rearrange symbolically for t:

    t=xˉ−μ0s/nt = \dfrac{\bar{x}-\mu_0}{s/\sqrt{n}}
  3. Step 3 — List the givens: sample mean (xbar) = 96.1000, hypothesized mean (mu0) = 96.4000, sample std dev (s) = 2.3000, sample size (n) = 26.0000.

  4. Step 4 — Substitute the given values:

    t=xˉ−μ02.3000/26.0000t = \dfrac{\bar{x}-\mu_0}{2.3000/\sqrt{26.0000}}
  5. Step 5 — Evaluate:

    t=−0.6651t = -0.6651
  6. Step 6 — Check: returning t = -0.6651 to

    t=xˉ−μ0s/nt = \dfrac{\bar{x}-\mu_0}{s/\sqrt{n}}

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

Answer:
t=−0.6651t = -0.6651

Why the other options are there

  • -1.3302 — kept a factor of two that cancels in the correct rearrangement.
  • -0.3325 — dropped that same factor in the other direction.
  • -0.7316 — rounded an intermediate value before the final step.

Reference: FE Handbook — Test Statistics

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