Hinton Press hypothesizes that the average life of its largest web press is 14,500 hours. They know

Question

that the standard deviation of press life is 2,100 hours. From a sample of 25 presses, the company
finds a sample mean of 13000 hours. At a 0.01 significance level, should the company conclude that
the average life of the presses is less than the hypothesised 14500 hours?

Answer 1

Z = (mean1 - mean2)/standard error (SE) of difference between means

SEdiff = √(SEmean1^2 + SEmean2^2)

SEm = SD/√n

If only one SD is provided, you can use just that to determine SEdiff.

Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability.