The top should be 11.3-10 and your denominator should be 3.1/(sqrt(60)). This is your critical value and the two-sided p-value is 2*P(Z>Zcrit).
This is the exercise:
The owner of a gas station wants to study gasoline purchasing habits by motorists at his station. He selects a random sample of 60 motorists during a certain week and the results were: Mean amount purchased X-bar = 11.3 gallons with std dev s=3.1.
At the 0.05 level of significance, is there evidence that the population mean purchased was different from 10 gallons? Find the confidence level and p-value at this level.
Did I set it up right.. Z = (10-11.3) / 3.1 = -0.42 ?
Thanks in advance.