<PRE><B>Question 1068633</B>
CI is 8000+/-t df=29,0.995 *300/sqrt(30); t value is 2.756
interval width is 2.756*300/sqrt(30)=150.95
(7849,8151)
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interval is 25=z*300/sqrt(n)
I use z, because the sample size is large, and I can always then use t for that df and see if it changes the result.
25=1.96*300/sqrt(n)
25 sqrt(n)=1.96*300=588
sqrt(n)=588/25=23.52
square both sides
n=553.19 round to 554. With this size sample, t=z.
When I use this in the calculator for a t-test, I get an interval of +/-25.</PRE>