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# S2 help watch

1. Wonder if anyone could be kind enough to help me ... revising for S2 retake on Tuesday and haven't done any stats since June

With continuous random variables, they give you a function e.g.

x/15 7 < x < 10
0 otherwise

And to find the E(X) you have to integrate x f(x). That's fine. But what do you do when there's more than one function? Which do you integrate, or is it both?

Any help much appreciated.
2. (Original post by emmings)
Wonder if anyone could be kind enough to help me ... revising for S2 retake on Tuesday and haven't done any stats since June

With continuous random variables, they give you a function e.g.

x/15 7 < x < 10
0 otherwise

And to find the E(X) you have to integrate x f(x). That's fine. But what do you do when there's more than one function? Which do you integrate, or is it both?

Any help much appreciated.
Say your given a pdf of

f(x) a < x < b
g(x) c < x < d

Then E(x) = Integral of x.f(x) between a and b, + Integral of x.g(x) between c and d.

Galois.
3. (Original post by Galois)
Say your given a pdf of

f(x) a < x < b
g(x) c < x < d

Then E(x) = Integral of x.f(x) between a and b, + Integral of x.g(x) between c and d.

Galois.
Thanks very much

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Updated: January 23, 2005
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