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.
Differential Leveling and Height of Instrument: FE Civil practice problem 2
During a constructability walkdown for the Westport parking structure green infrastructure project, the hydraulics analyst runs a level loop from benchmark elevation 543.75 ft with backsight 3.74 ft and foresight 5.38 ft. What turning point elevation is computed?
- A542.11 ft
- B334.34 ft
- C601.38 ft
- D699.99 ft
Show the answer and worked solution
Answer: A — 542.11 ft
Worked solution
- Step 1. Compute height of instrument
HI = BM + BS
HI = 543.75 + 3.74 = 547.49 ft
- Step 2. Subtract foresight
elevation = HI - FS
elevation = 547.49 - 5.38 = 542.11 ft
Why the other choices are wrong
- Choice B
- This figure lands roughly 38% lower than the correctly reduced elevation of 542.11 ft; that gap cannot be traced to one clean substitution of the backsight (3.74 ft) or foresight (5.38 ft), so the height of instrument should be formed as 543.75 + 3.74 = 547.49 ft before subtracting the foresight to obtain 542.11 ft.
- Choice C
- This value sits about 11% above the correctly reduced elevation of 542.11 ft; it does not follow from any single sign or reading error on the backsight (3.74 ft) or foresight (5.38 ft), so the turning point elevation comes from 547.49 ft height of instrument minus the 5.38 ft foresight, giving 542.11 ft.
- Choice D
- This total runs about 29% above the correctly reduced elevation of 542.11 ft; no single misread of the backsight (3.74 ft) or foresight (5.38 ft) reproduces it, so recompute the height of instrument as 543.75 + 3.74 = 547.49 ft and then subtract the foresight to reach 542.11 ft.