What are the excel formulas to solve this if the number I pick is 80?

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 thesquare 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 ands 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

This will be typed into an excel cell to find E and then take the =xbar + E and =xbar - E

=confidence.norm(.05,6,100)

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.)