# Discrete Random Variables

• May 21st 2009, 02:53 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, 03:14 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, 02:25 AM
I-Think
Silly statistician, integration is for continuous random variables(Doh).