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# Coded mean help pleeease !! watch

1. Heyy Guys
Okay so basically i am really struggling on the whole coded mean/coded standard deviation thing in maths S1, so seeing as TSR is full of ridiculously smart people i was wondering if any of you would be able to explain the method to me ?
Im sure that once i understand it i will be able to do it fine, i just cant get my head around it atm !!
Any help greatly appreciated, just a simple method would be a huuuge help !! Thanks in advance

And PS yes my teacher has taught us this but she is a baaad teacher and i totally didnt get it !!
2. the idea of coding is to make arithmetic a little less difficult or painful.

if we have a discrete random variable X with a mean of E(X), we can calculate it more easily by coding, as X may have terms with many digits or with large numbers, or very small numbers.

If we code it linearly in the way ax + b, the mean of the coded X, ie E(ax+b) = aE(X) + b, and as we said before, the coded one is easier to calculate, so if we find aE(X) + b, all we have to do to make it into E(x) is minus b and divide by a, you see?

Spoiler:
Show
if you were curious, we can prove that E(ax+b) = aE(X) + b

say that

so

but and as there are n b's and so n*b/n = b

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Updated: November 10, 2008
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