# Discrete Random Variables

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• May 21st 2009, 03:53 PM
I-Think
Discrete Random Variables
Hi. Glad to see that we're being reminded of the rules. Here's a question on random variables.

The discrete random variable X has a probability density function

$
P(X=x)= \frac{x}{10} where x= 1, 2, 3, 4
$

P(X=x) is 0 otherwise

If $Y$denotes the sum of two independent observations of $X$
Determine the value of $P(Y=4)$
• May 21st 2009, 04:14 PM
Plato
Quote:

Originally Posted by I-Think
The discrete random variable X has a probability density function $
P(X=x)= \frac{x}{10} where x= 1, 2, 3, 4$

P(X=x) is 0 otherwise
If $Y$denotes the sum of two independent observations of $X$
Determine the value of $P(Y=4)$

Note that elementary event Y=4 is simply {(1,3),(3,1),(2,2)}.
Calculate the probabilities of each and add.
• May 22nd 2009, 03:25 AM
I-Think
Silly statistician, integration is for continuous random variables(Doh).

Sorry about this question, for some strange reason I thought this was a continuous random variable, and continued in this erroneous belief even after your help.(Headbang)

Oh well, everybody makes mistakes in life, and maths.

Thanks for your help. (Please don't remind me of the thread's title)