If in fact none of the 20 formulations have any effect on wear, what is the probability that H_{0} will be rejected for one or more of them?
We first find the probability that the right conclusion (not rejecting H_{0}) is made for all the formulations. For each formulation, the probability that H_{0} is not rejected is 1 − 0.05 = 0.95, so the probability that H_{0} is not rejected for any of the 20 formula-tions is (0.95)^{20} = 0.36. The probability is therefore 1 − 0.36 = 0.64 that we incorrectly reject H_{0} for one or more of the formulations.