A used car dealership surveyed 50 customers who bought a card from them two years ago. 78% of customers said that they would recommend this dealership to their friends. What is the 90% confidence interval for the percent of all former buyers who would recommend this dealership to their friends

The 90% confidence interval for the percent of all former buyers who would recommend this dealership to their friends is (68.36%, 87.64%).

Step-by-step explanation:

In a sample with a number n of people surveyed with a probability of a success of , and a confidence level of , we have the following confidence interval of proportions.

In which

z is the z-score that has a p-value of .

A used car dealership surveyed 50 customers who bought a card from them two years ago. 78% of customers said that they would recommend this dealership to their friends.

This means that .

90% confidence level

So , z is the value of Z that has a p-value of , so .

The lower limit of this interval is:

The upper limit of this interval is:

As a percent:

0.6836*100% = 68.36%

0.8764*100% = 87.64%

The 90% confidence interval for the percent of all former buyers who would recommend this dealership to their friends is (68.36%, 87.64%).

step-by-step explanation:

once you graph it hit 2nd (the blue button) and graph

that takes you to a table of coordinates

on the left is x coordinates and on the right is y coordinates and an empty box

(you may have to scroll up/down in order to get ( x, 0)