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# Mean and Variance Watch

1. ;

I have calculated the mean as 71/15

I calculated the sample variance as 82/105

But then to calculate and , I know that:

Giving my value of p

And I can then work out as:

Which really doesn't seem right.

I spoke to someone on my course, and he got:

But I'm really not sure how.

Can anyone point out where I've gone wrong?

Cheers
2. Okay, I can see how he got

But this still doesn't explain to me how he got

Obviously, my Variance is wrong, but I calculated the sample variance with the correct method:

Really stuck on this, and can't see where :/
3. The only way I can see for this is that we know that n must be integer, so having calculated it as 5.66 we round to 6, and then use p = mean/n. This gives the (n,p)=(6,71/80) result. (Your calculations are correct.)

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Updated: April 6, 2013
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