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Over a very long period of time, it has been noted that on Friday's 25% of the customer at the drive in window at the bank make a deposit. What is the probability that it takes 4 customers at the drive in window before the first one makes a deposit

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kvnmurty
As I understand the question, the 1st, 2nd, and 3rd customers do not make a deposit, and 4th one makes  a deposit.   If it is the fifth customer to make a deposit, then you can change accordingly.

Probability that a customer makes a deposit = 25% = 1/4.
Probability that a customer does not make a deposit = 3/4

  We assume that one customer making a deposit is not dependent on another making a deposit. 

Probability needed = 3/4 * 3/4 * 3/4 * 1/4 = 27/256


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