## statistical testing - finding the interval estimate

17) Michele wishes to give a confidence interval for the percentage of Illinois
residents who agree with a certain law. She questions 1500 people from a good
sample and and that 960 agree with the policy. If she chooses a confidence level of
.91, what should her interval estimate for the percentage of people who agree with
this law be? (You may assume that the population of Illinois is in finite.)
A:

I calculated the mean to be .64
The estimated population standard deviation to be .48
The standard deviation to be .4804

When I plug all that in to the formula to get the standard error formula, I get the wrong answer. The teacher says the outcome should be between .61 and .66

18)
(a) What interval estimate for a population parameter M can one get for a confi dence interval of .80? (Express the interval in terms of x (the sample mean) and ox (standard error of the sampling distribution.))
A:

I divided 80/2 = 40 which gives a Z value = 1.7

That is all I know for that one.