Chapter 10.2, Problem 4Q

An army enlistment officer categorizes potential recruits by IQ into three groups- class I: $<\text{ 9}0$ class II: $90-110$, and class III: $\text{>11}0$. Given that the IQs in the population from which the recruits are normally distributed with $\mu =100$ and $\sigma =16$, calculate the probability that of seven enlistees, two will belong to class I, four to class II, and to class III.