Answer:
The 85% confidence interval for the population proportion of tenth graders reading at or below the eighth grade level is (0.259, 0.301).
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 .
For this problem, we have that:
972 students, 700 read above the eight grade level. We want the confidence interver for the proportion of those who read at or below the 8th grade level. 972 - 700 = 272, so
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 of tenth graders reading at or below the eighth grade level is (0.259, 0.301).