Answer:
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).