john sells magazine to raise money for poor peoples. the probability of making a sales is independently, 0.09 for each person he approaches.given that he approaches 10 people what is the probability that he will make exactly 5 sales?
s is sale , n is no sale ... this is a binary probability
... p(s) + p(n) = 1
you want the 5th term of the expansion ... (s + n)^10
... 10C4 s^5 n^5 = 10C4 (.09^5) (.91^5) = ?