Central Limit Theorem

Apr 2010
30
0
See Question 3 on the attached document....

It is a past exam paper but the solutions are not provided so i cant see where i am going wrong....

I derived the PGF in part (i) then proceeded to get E(x) as 11/5 and Var(x) = 39/25

The problem is in part (iii) in the central limit theorem. I constructed the sample mean as (11/5)*50 to give 110 and the variance as \(\displaystyle {\frac {\sigma}{\sqrt {n}}}\) which i got as such a small value (sqrt39/25)/(sqrt50) that it made my Z values so large that phi of these values were like 56 and -320 which would obviously be approximately 1-0, meaning almost the whole of the set is in this interval.... anyway it didnt seem right! have i gone wrong somewhere?
 

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matheagle

MHF Hall of Honor
Feb 2009
2,763
1,146
I'm not sure what you're asking.

I get \(\displaystyle E(X)=2.2\) and \(\displaystyle E(X^2)=6.4\)

So \(\displaystyle V(X)=1.56\)

Thus \(\displaystyle Y\approx N((50)(2.2), (50)(1.56))\)

Since the X's are integer based you may want to put in a correction factor, but that won't
alter your answer a whole lot.