Question

There is an urn containing 10 marbles numbered 1 to 10. We sample 4 marbles without replacement. What is the probability that our sample contains the marbles labeled 1 and 2

Answer 1

Explanation:

The easiest way to do this is to assume you don't get a 1 or 2. You make your first draw from 8.

8 * 7 * 6 * 5 = 1680

The total number of ways of drawing 4 marbles is

10*9 * 8 * 7 = 5040

P(`(1 or 2) ) = 1680 / 5040 = 0.33333

The probability of getting a 1 or 2 in 4 throws = 1 - 0.3333 = 0.66667