In a study, the mean serum cholesterol is 200 mg/dL with a standard deviation of 20 mg/dL. What percentage of the population would be expected to have cholesterol levels between 160 and 240 mg/dL, assuming a normal distribution?
- A 68.2%
- B 95.4% ✓
- C 99.7%
- D 50%
Correct answer: B. 95.4%
Explanation
In a normal distribution, mean ± 2 SD encompasses 95.4% of the population. Here 160 = 200 - 2×20 and 240 = 200 + 2×20, so the range spans exactly 2 SDs on each side. Mean ± 1 SD = 68.2% (180–220 mg/dL); mean ± 3 SD = 99.7% (140–260 mg/dL). This is the empirical rule (68-95-99.7 rule) for normal distributions, tested frequently in NEET PG biostatistics.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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