# Confidence Interval for Proportion

3 Questions

QUESTION 1 of 3

Hi professor. I keep getting stuck in the same problems. My confusion is when I watch the videos and it display how to do the work on a graphing calculator. Could you please go through problem 58 from 7.6, and show me the steps without the graphing calculator? I could do the earlier problems from that section but 58 and the following few problems Im struggling with when the n is given instead of the ^P .

QUESTION 2 of 3

Hello professor, I was doing the new review questions for chapter seven #75 and the result I got for the population proportion interval were 67.12 % and 76.48 %. Your answer says the results are 74.8% and 83.2%, because my Z score for .02/2 = 2.326 my p^= .718 and q^=.282 and my E=.046807. Can you please tell me where is the mistake? I've done the problem 3 times already. Thank you.

QUESTION 3 of 3

For the question below, I got 0.001 and 0.049. The solution has 0.003, 0.047. Can you explain how to do this one?

Assuming that grades in a statistics class are normally distributed with a mean of 75 and a standard deviation of 20, there should be around 5% of the students who earn a C-. In a recent study of a class of 200 students there were 5 grades of C-. Construct the 95% confidence interval for the true proportion of C- grades for statistics classes like the class used in the study 200. If the class grades were normally distributed with a mean of 75 and a standard deviation of 20, we'd expect that around 10 grades (5% of 200) would be in the C- range. Looking at the interval we just created, what do you think about the idea that the grades are normally distributed?