A process for a certain type of ore is designed to reduce the concentration of impurities to less than 2%. It is known that the standard deviation of impurities for processed ore is 0.6%. Let μ represent the mean impurity level, in percent, for ore specimens treated by this process. The impurity of 80 ore specimens is measured, and a test of the hypothesis H₀ : μ ≥ 2 versus H₁ : μ < 2 will be performed.

a. If the test is made at the 5% level, what is the rejection region?

b. If the sample mean impurity level is 1.85, will H₀ be rejected at the 10% level?

c. If the sample mean pH is 1.85, will H₀ be rejected at the 1% level?

d. If the value 1.9 is a critical point, what is the level of the test?