The emission of 10 engines is found to be:
15.6, 16.2, 22.5, 20.5, 16.4, 19.4, 16.6, 17.9, 12.9, 13.9.
The mean emission must, according to regulations, be u (mean) greater than 20 parts per million. Test this at a significance level of a equal to 0.01
Find the mean first = sum of scores/number of scores
Subtract each of the scores from the mean and square each difference. Find the sum of these squares. Divide that by the number of scores to get variance.
Standard deviation = square root of variance
Z = (score-mean)/SEm
SEm = SD/√n
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. Is it significant?