Question

Two balls are drawn in succession without replacement from an urn containing 4 red balls and 5 blue balls.Let R be the random variable representing the number of red balls.Find the values of the random variable R.

Answer 1

Let R stand for a red ball

Let B stand for a blue ball

When two balls are selected at random without replacement, the sample space is,

$S=\{RR, RB, BR, BB\}$

We have the following cases

1. The sample point RR shows that both balls picked are red, so $R=2$
2. The sample points RB and BR shows that one of the balls picked is red so, $R=1$
3. The sample point, BB shows that non of the balls picked is red so, $R=0$

From the 3 cases above, we can observe that the random variable R is discrete and may take on the values 0,1,2. That is, $r=0,1,2$