单选题 Given a normally distributed population with a mean income of $40000 and standard deviation of $ 7500, what percentage of the population makes between $ 30000 and $ 35000?

A. 15.96.
B. 13.34.
C. 41.67.

【正确答案】 A

【答案解析】The z - score for $ 30000 = ($ 30000-$ 40000)/$ 7500 or - 1.3333, which corresponds with 0.0918. The z - score for $ 35000 = ($ 35000-$ 40000)/$ 7500 or -0.6667, which corresponds with 0.2514. The difference is 0.1596 or 15.96%.