I need someone to explain HOW to do this..I don't want just the answer I have got to figure out how to do this before my mid-term, and I'm completely clueless!

Question

3. One of the major U.S. tire makers wishes to review its warranty for their rainmaker tire. The warranty is for 40,000 miles. The tire company believes that the tire actually lasts more than 40,000 miles. A sample 49 tires revealed that the mean number of miles is 45,000 miles with a standard deviation of 15,000 miles. Test the hypothesis with a 0.05 significance level.

Answer these questions:

3a) What is the H0? Null hypothesis, hypothesis about a population of the relationship among populations
3b) What is the H1? alternative hypothesis, hypothesis about parameters that is accepted if the null hypothesis is rejected
3c) What is the decision rule?
3d) What is the calculated value of z?
3e) What is your decision?

Answer 1

Ho: mean = 40,000

H1: mean > 40,000

Z = (score-mean)/SEm

SEm = SD/√n

Since you are only concerned with greater than 40,000, you will reject Ho if Z falls in the top 5%.
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability related to the Z score.

I'll let you calculate Z and come to your own decision.