The answer to number 1 above covers this. I graded on whether your essay was readable and logically self-consistent. Use a method similar to the Drake equation to estimate the number of people getting a haircut at some given moment. That is, multiply the probabilities of each such event times the number of people in, for example, the United States. I estimate that there are about 60,000 people in Bloomington.
People get their hair cut about once a month.
Examining the phone book I counted about 130 Barber Shops and Beauty Salons.