Question: Thank you in advance for the help. Hi,You have an test that produces a falsepositive result with probability 0.05, and hence the probability of not obtaining a falsepositive is 0.95. Suppose that you perform n, independent repetitions of the test and X is the number of falsepositives you obtain. The probability that X is greater than or equal to 1, is 1 minus the probability that X is less than 1. That is Hence if P(X >= 1) <= 0.2 then 1  P(X = 0) <= 0.2 and hence P(X = 0) >= 0.8. Thus you want the largest n so that P(X = 0) >= 0.8. Since the probability of not obtaining a falsepositive is 0.95 and the tests are independent, the probability of no falsepositives in the n tests is 0.95^{n}. Thus you want the largest n so that 0.95^{n} >= 0.8. Now use your calculator to find 0.95^{1}, 0.95^{2}, ... and see how large the exponent can be before 0.95^{n} is smaller than 0.8. Cheers,Harley
