You should be able to integrate these, but that's not the point of these problems.

AND an exponentially distributed rv is nonzero on ZERO to infinity.

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- Mar 6th 2010, 01:41 AM #1

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## E(x^2) and V(x^2)

Explosive devices used in mining operations produce nearly circular craters when detonated. The radii of these craters are exponentially distributed with mean 10 feet. Find the mean and variance of the areas produced by these explosive devices.

I tried to derive

E(pi X^2) and Var ( pi X^2) where E(X)=10 using the formula

E(X) = integrate (X. i/r. exp (-x/r) ) from neg infinity to infinity but i couldnt get the answer...

thanks!

- Mar 6th 2010, 07:17 AM #2

- Mar 6th 2010, 08:06 AM #3

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- Mar 6th 2010, 08:24 AM #4

- Mar 7th 2010, 12:34 AM #5

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- Mar 7th 2010, 07:36 AM #6
I answered that question here

http://www.mathhelpforum.com/math-he...tml#post469524