# Thread: Compute the z or t value of the sample test statistic.

1. ## Compute the z or t value of the sample test statistic.

In an article appearing in Today’s Health a writer states that the average number of calories in a serving of popcorn is 75. To determine if the average number of calories in a serving of popcorn is different from 75, a nutritionist selected a random sample of 20 servings of popcorn and computed the sample mean number of calories per serving to be 78 with a sample standard deviation of 7.

2. Originally Posted by mathretard
In an article appearing in Today’s Health a writer states that the average number of calories in a serving of popcorn is 75. To determine if the average number of calories in a serving of popcorn is different from 75, a nutritionist selected a random sample of 20 servings of popcorn and computed the sample mean number of calories per serving to be 78 with a sample standard deviation of 7.
Where is the trouble in calculating t?

You substitute the given values into the formula $t = \frac{\overline{x} - \mu_0}{s/\sqrt{n}}$.

3. ## additional question

So is the answer t= 1.916 or z=1.916

4. Originally Posted by mathretard
So is the answer t= 1.916 or z=1.916
You cannot use z because the population variance is unknown and the sample size is small.

I haven't checked the answer - I assume you can correctly use a calculator.