In a department store there are 120 customers, 90 of whom will buy at least one item. If 5 customers are selected at random, one by one, find the probability that all will buy at least one item.
Now I know that I must subtract the probability of the 90 from 1. but EH? why cant I do that?
the answer in the book is 243/1024 but it does not show how it got there.
yay math love!