SOLUTION: 18 out of 20 customers make a purchase. If three customers are selected randomly one at a time, what is the probability that all will make a purchase? Please help.

Question 149861: 18 out of 20 customers make a purchase. If three customers are selected randomly one at a time, what is the probability that all will make a purchase?
Please help.
Answer by scott8148(6628) (Show Source): You can put this solution on YOUR website!
there are 20C3 (1140) possible groups of 3 in 20 __ some of these groups contain non-purchasers

there are 18C3 (816) possible groups of 3 in 18 __ none of these groups contain non-purchasers

probability of all purchasers is 816/1140 or 0.716 (approx)

if order of selection is thought to be important (permutation vs combination); the result will be the same
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