Original question written by FE Exam AI Prep from the public FE Civil exam specification. Before release, a solver model re-derived the answer twice from the question alone, without its answer key, and a critic model checked the result, and the arithmetic was re-run as an executable calculation. No licensed engineer reviews these questions. It is not an NCEES question and does not come from any NCEES practice exam. FE Exam AI Prep is an independent study tool and is not affiliated with, endorsed by, or sponsored by NCEES.
Standard Error of the Mean: FE Civil practice problem 3
For the Cedar Grove industrial service road, a survey coordinator preparing a constructability analysis has a sample standard deviation of 240 psi from 32 concrete tests. What is the standard error of the sample mean?
- A24.71 psi
- B42.43 psi
- C32.28 psi
- D47.16 psi
Show the answer and worked solution
Answer: B — 42.43 psi
Worked solution
- Step 1. Use standard error of the mean
SE = s/sqrt(n)
- Step 2. Substitute values
SE = 240/sqrt(32) = 42.43 psi
Why the other choices are wrong
- Choice A
- This figure is well above the value that SE = s/sqrt(n) gives for a sample standard deviation of 240 psi across 32 concrete tests, so it does not correspond to dividing 240 by the square root of 32; the standard error should be recomputed directly from those two stated figures.
- Choice C
- This figure is slightly above the value that SE = s/sqrt(n) gives for a sample standard deviation of 240 psi across 32 concrete tests, so it does not correspond to dividing 240 by the square root of 32; the standard error should be recomputed directly from those two stated figures.
- Choice D
- This figure is moderately below the value that SE = s/sqrt(n) gives for a sample standard deviation of 240 psi across 32 concrete tests, so it does not correspond to dividing 240 by the square root of 32; the standard error should be recomputed directly from those two stated figures.