Question 6.18: If only one formulation were tested, and it in fact had no e...

If the formulation bas no effect on wear, then μ = 100 μm, so H_0 is true. Rejecting H_0 is then a type \text{I} error. The question is therefore asking for the probability of a type \text{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 μ = 100 is on the boundary of H_0, the probability of a type \text{I} error is equal to the significance level. The probability is 0.05 that H_0 will be rejected.