Problema Solution
. In a shop there are 20 customers, 18 of whom will make a purchase. If three customers are selected, one at a time, at random, what is the probability that all will make a purchase?
Answer provided by our tutors
no. of ways in which 3 customers can be selected out of 20 = 20C3
no. of ways in which 3 customers can be selected such that each one of them make a purchase (select any any 3 from 18 customers who are making a purchase ) = 18C3
therefore,
probability of favourable occurances = 18C3/20C3
(i.e. all 3 will make purchase) = (17 x 16)/(20 x 19) = 272/380 = 68/95