Last year, the mean time taken by students at a school to complete a certain test was 25 minutes. Akash believes that the mean time taken by this year's students was less than 25 minutes. In order to test this belief, he takes a large random sample of this year's students and he notes the time taken by each student. He carries out a test, at the 2.5% significance level, for the population mean time, μ minutes. Akash uses the null hypothesis H0: μ = 25.

1. (a)Give a reason why Akash should use a one-tailed test.[1]
2. (b)Akash finds that the value of the test statistic is z = -2.02. Explain what conclusion he should draw.[2]
3. (c)In a different one-tailed hypothesis test the z-value was found to be 2.14. Given that this value would lead to a rejection of the null hypothesis at the α% significance level, find the set of possible values of α.[3]
4. (d)The population mean time taken by students at another school to complete a test last year was m minutes. Sorin carries out a one-tailed test to determine whether the population mean this year is less than m, using a random sample of 100 students. He assumes that the population standard deviation of the times is 3.9 minutes. The sample mean is 24.8 minutes, and this result just leads to the rejection of the null hypothesis at the 5% significance level. Find the value of m.[3]