Major software manufacturers offer a helpline that allowscustomers to call and r

Question

Major software manufacturers offer a helpline that allowscustomers to call and receive assistance in solving their problems.However, because of the volume of calls, customers frequently areput on hold. One software manufacturer claims that only 20% ofcallers are put on hold. Suppose that 100 customers call. What isthe probability that more than 25 of them are put on hold?

The answer is .8747 I need to know how

Explanation / Answer

p = 0.2 hence q = 1-0.2 = 0.8 n = 100 mean, = np = 100 x 0.2 = 20 standard deviation, = npq = (100x0.2x0.8) =4 P(X>25) P(Z>(X-)/)= P(Z>(25-20)/4) = 1-0.8944    (from z table) = 0.1056 hence probability that more than 25 of them are put on hold =0.1056

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