A university bookstore claims that 50% of its customers are satisfied with the service and prices.
a. If this claim is true, what is the probability that in a random sample of 600 customers less than 45% are satisfied?
b. If you would reject the bookstore’s claim if the probability computed in a. will be less than 0.05%, how many customers at least should have expressed satisfaction?
a. We denote the (population) probability that is claimed by the bookstore as and the probability computed by the sample as . Then:
b. In this case we have to compute from . From table 3 in appendix B-8 we find . So, we have to solve from the equation: and we get: and thus the number of customers expressing satisfaction should be at least 280.