Question

3. Nutrition labels. The nutrition label on a bag of potato chips says that a one ounce (28 gram) serving of potato chips has 130 calories and contains ten grams of fat, with three grams of saturated fat. A random sample of 35 bags yielded a sample mean of 134 calories with a standard deviation of 17 calories. a. Calculate the 95% confidence interval of for this random sample. Then interpret this interval.

Answer 1

The 95% confidence interval of for this random sample is between 128.16 calories and 139.84 calories. This means that we are 95% that the mean number of calories for all bags of potato chips is in this interval.

Explanation:

We have the standard deviation for the sample, which means that the t-distribution is used to solve this question.

The first step to solve this problem is finding how many degrees of freedom, we have. This is the sample size subtracted by 1. So

df = 35 - 1 = 34

95% confidence interval

Now, we have to find a value of T, which is found looking at the t table, with 34 degrees of freedom(y-axis) and a confidence level of
`1 - (1 - 0.95)/(2) = 0.975`. So we have T = 2.0322

The margin of error is:

`M = T(s)/(√(n)) = 2.0322(17)/(√(35)) = 5.84`

In which s is the standard deviation of the sample and n is the size of the sample.

The lower end of the interval is the sample mean subtracted by M. So it is 134 - 5.84 = 128.16 calories

The upper end of the interval is the sample mean added to M. So it is 134 + 5.84 = 139.84 calories

The 95% confidence interval of for this random sample is between 128.16 calories and 139.84 calories. This means that we are 95% that the mean number of calories for all bags of potato chips is in this interval.