The travel-to-work time for residents in Ventura County is unknown. Assume the population variance is 39. How large should a sample be if the margin of error is 1 minute for a 93% confidence interval

A sample size of 128 is needed.

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 Ztable as such z has a pvalue of .

So it is z with a pvalue of , so

Now, find the margin of error M as such

In which is the standard deviation of the population(square root of the variance) and n is the size of the sample.

How large should a sample be if the margin of error is 1 minute for a 93% confidence interval

We need a sample size of n, which is found when . We have that . So

Rounding up

A sample size of 128 is needed.

step-by-step explanation:

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