Industrial Engineering · Work System Design · 2 marks · Numerical answer
A work-sampling study with 100 observations found 25% worker idle time. Find the number of observations required for ±10% accuracy at 95.45% confidence (integer).
For a proportion p = 0.25 and two-sigma confidence, $n=4p(1-p)/e^2$. If accuracy means absolute ±0.10, n = 4(0.25)(0.75)/0.10² = **75**. If it means ±10% of p, e = 0.025 and n = **1200**. The wording permits both conventions; the final key accepts **71–76 OR 1150–1210**, preserved as two separate intervals. These are total required sample counts.
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