Stats unit review, (confidence intervals)

This is a piece of the STATS unit review.
Confidence intervals.

A confidence interval is… “Predicting the likelihood that the mean of a sample occurs within a certain interval, a certain percent of the time”.

90%...95%...99%... sizes of confidence intervals considered “worthwhile” for statistical prediction purpose.

Here is an example question:
A research study on fruit flies found that an average of 50% of them stay alive after 32 hours.

a) Determine the 95% confidence interval for the percentage of a sample of 1000 fruit flies still alive after 32 hours. Show your work.
Here is what you do.

In your calculator, press the buttons… STAT then TESTS. Go to Prop z-int and it brings up this screen.
X:
N:
C-Level:
Calculate

X is your mean, N is your total number, so in this example your X would be 500, and your N would be 1000. Your C-level is 95. Press calculate and you should get this screen.
1-PropZInt
(.046901,.053099)
P=.5
N=1000

Your percentage interval is (.046901,.053099)
After every question you need to explain the meaning of the confidence interval. So in this example you would write….

If a similar experience/survey/poll were conducted this interval (46.9, 53.1) means that we are 95% confident that 32 hours later out of the 1000 fruit flies between 46,9 and 53.1 percent of them will remain alive.

I hope you are confident with this part of the unit, and if you have any questions please place them in the comments section and I will do my best to answer them.