# Probability problem

1. Jan 29, 2009

### kasse

8 balls are in a box. Each ball can be either blue or red. If there are d red balls in the box, calculate the probability p(d) that two randomly selected balls from the ball are both blue. Sketch p(d).

$$p(d) = \frac{_{8-d}C_{2}*_{d}C_{0}}{_{8}C_{2}} = \frac{_{8-d}C_{2}}{14}$$

Is this correct? Is there a better way to write it so that I can sketch p(d)?

Last edited: Jan 29, 2009
2. Jan 29, 2009

### tiny-tim

Hi kasse!

P(1st = blue) times P(2nd = blue | 1st = blue)

3. Jan 29, 2009

### kasse

Of course!

Last edited: Jan 29, 2009