## Need to know which formulae which has been used

Standard deviation, mean, variance, z-scores, t-tests, etc.
zorro
Posts: 28
Joined: Sat Jun 12, 2010 9:26 am
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### Need to know which formulae which has been used

Question :

The average working-set size X of a program is normally distributed with the unknown mean $\mu$ and a known variance $\sigma$2=81 . The program was executed 36 times and the average working set size for each run recorded. The sample mean was computed to be 100 page frames . Assuming successive runs of the program are independent, find the 95% confidence interval for the mean average working set size

Solution:

(100-1.96 * 9/6 , 100 + 1.96 * 9/6) = (97.06 , 102.94)

Need to know which formula been used in order to get this result?

maggiemagnet
Posts: 358
Joined: Mon Dec 08, 2008 12:32 am
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### Re: Need to know which formulae which has been used

If you're not sure what formula this is, try working backwards from the "sample" formulas they've given you. Which one uses $\sqrt{\sigma^2}\, =\, \sigma$ in the numerator? Which one also uses $\sqrt{n}$ in the denominator?

zorro
Posts: 28
Joined: Sat Jun 12, 2010 9:26 am
Contact:

### Re: Need to know which formulae which has been used

If you're not sure what formula this is, try working backwards from the "sample" formulas they've given you. Which one uses $\sqrt{\sigma^2}\, =\, \sigma$ in the numerator? Which one also uses $\sqrt{n}$ in the denominator?
Thanks!!