# Probability question ,Random variables and probability distribution

1. Nov 8, 2012

### tj00343

I'm completely lost on this probability problem,

1. The problem statement, all variables and given/known data

A Box contains 5 indiscernible CDs.It is known that among them 2 are for children .So in order to find the first children's CD ,they are tested one after the other (successively ),Denote by X the random variable which represents the number of tests until the first children's cd is spotted

1- List all the possible values of X

2-Determine the probability distribution of X

3- Calculate the probability that at least 2 tests were performed

2. The attempt at a solution

1- x={1 2 3 4 }
2- very lost here
3- I can't solve without part 2

thank you

Last edited: Nov 8, 2012
2. Nov 8, 2012

### vela

Staff Emeritus
Is this a trick question? They're CDs, so you'll never spot a book.

You should be able to tell us the probability that X=1.

3. Nov 8, 2012

### Ray Vickson

You should also be able to tell us the probability that X = 2. After that, you should be able to do X = 3 and X = 4.

RGV