On the first one we will have a 95% confidence interval with z=1.96 and n=100
Pick a number for xbar between 60-100. Pick a number for s between 4-8. Find the confidence interval given
xbar +/- E
Note to find the square root of n use n^.5 where you are raising to the .5 or 1/2 power which is a square root. You can also use the square root key.
Here is a short cut to use excel!!!
Pick a value for xbar and s and work it first with n=100 and then with n=400. Let’s say you pick xbar = 80 and s=6. Since you have a 95% confidence interval alpha = 100%-95% =5% or .05 as a decimal n is 100.
This is a z score so we use =confidence.norm(alpha, sd, n) to find E
In this case you will type this in an excel cell to find E and then take the =xbar + E and =xbar – E
then hit enter
Instead of 100 let n=400
Show both intervals and the numbers you used. Why do you think they changed?
(If you had a t test where n< 30 then do then use the following
=confidence.t(alpha,sd,n) to find E.)