It is desired to estimate the average time it takes Statistics students to finish a computer project to within two hours at 90% reliability. It is estimated that the standard deviation of the times is 14 hours. How large a sample should be taken to get the desired interval? n = 231 n = 189 n = 325 n = 133

n = 133.

Step-by-step explanation:

We have that to find our level, that is the subtraction of 1 by the confidence interval divided by 2. So:

Now, we have to find z in the Z-table as such z has a p-value of .

That is z with a pvalue of , so Z = 1.645.

Now, find the margin of error M as such

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

Standard deviation of the times is 14 hours.

This means that

How large a sample should be taken to get the desired interval?

Within 2 hours, which means that we want n for which M = 2. So

Dividing both sides by 2

Rounding up, n = 133.