If only one formulation were tested, and it in fact had no effect on wear, what is the probability that H_{0} would be rejected, leading to a wrong conclusion?
If the formulation has no effect on wear, then ๐ = 100 ๐m, so H_{0} is true. Rejecting H_{0} is then a type I error. The question is therefore asking for the probability of a type I error. In general, this probability is always less than or equal to the significance level of the test, which in this case is 5%. Since ๐ = 100 is on the boundary of H_{0}, the probability of a type I error is equal to the significance level. The probability is 0.05 that H_{0} will be rejected.