Insurance companies are interested in knowing the population percent of drivers who always buckle up before riding in a car. They randomly survey 391 drivers and find that 319 claim to always buckle up. Construct a 85% confidence interval for the population proportion that claim to always buckle up.

The 85% confidence interval for the population proportion that claim to always buckle up is (0.7877, 0.8441).

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 zscore that has a pvalue of .

They randomly survey 391 drivers and find that 319 claim to always buckle up.

This means that

85% confidence level

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

The lower limit of this interval is:

The upper limit of this interval is:

The 85% confidence interval for the population proportion that claim to always buckle up is (0.7877, 0.8441).

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