As a store manger you would like to find out the average time it takes to unload the truck which delivers the merchandise for your store. For this purpose, you have taken a random sample of 35 days and found the average unload time to be 204 minutes for the sample. You also found that the standard deviation is 30 minutes for the sample. Find the upper boundary of the 95% confidence interval for the average unload time. Round the answer to two decimal places.

The upper boundary of the 95% confidence interval for the average unload time is 264.97 minutes

Step-by-step explanation:

We have the standard deviation for the sample, but not for the population, so we use the students t-distribution 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 = 35

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 ). So we have T = 2.0322

The margin of error is:

M = T*s = 2.0322*30 = 60.97

The upper end of the interval is the sample mean added to M. So it is 204 + 60.97 = 264.97

The upper boundary of the 95% confidence interval for the average unload time is 264.97 minutes

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step-by-step explanation:

the 4th choice is the correct one

step-by-step explanation: