SOLUTION: Still struggling with this one. There are 20 customers. 18 will make a purchase. If three customers are selected, one at a time, what is the probability that all will make a purcha

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Question 149737: Still struggling with this one. There are 20 customers. 18 will make a purchase. If three customers are selected, one at a time, what is the probability that all will make a purchase? Instructor says the answer is one of four 1)0.7717, 2) 0.7605 3) 0.8524 or 4)0.8808
Please help
Answer by scott8148(5895) About Me  (Show Source):
You can put this solution on YOUR website!
would be interested in seeing the instructor's solution

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