An elevator has a weight capacity of 4000 pounds. Assume that the weight X
of a randomly selected person is normally distribution with mean 180 pounds
and standard deviation of 25 pounds. What is the maximum number N of people
allowed on the elevator such that the probability of their combined weight
exceeding the 4000 pound load limit is less than 5%
根据 (x-µ)/δ 来做正态分布分析，设N个人满足达到条件，那末这样µ=
180N, δ=? 是25N？ 怎莫算来得到variance 呢谢谢
