The routes of postal deliverers have been carefully planned so that each deliverer works between 7 and 7.5 hours per shift. The planned routes assume an average walking speed of 2 miles per hour and no shortcuts across lawns. In an experiment to examine the time deliverers actually spend completing their shifts, a random sample of 75 postal deliverers was secretly timed.

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What is the Null Hypothesis in this case?

What is the sample mean Xbar =?

What is the sample standard deviation?

Now, our sample shows the average is less than 7 hours but is this less amount significant?

(We know that if our average is 6.999, we most likely will say that there is no difference, but how about 6.998, 6.997, .... so it is up to a point that we have to say it becomes significant, how to find it out?);

We need to first calculate the standard error, you can use the formula S/Sqrt(n), n = 75.

What is the test statistics, that is (Xbar-mu)/SE =

What is the p-value? (Note: since your calculated t-value is negative which can't be used in the formula, just ignore the negativesign and enter the positive t-value in the formula).

Remember, if the p-value is smaller than 5% in most of the cases, we are happy and jump to reject the NULL and accept the alternative hypotheses, that is the difference from 7 hours is indeed significant with only less than 5% of wrong and 95% right.