Question

A bag contains 4 red marbles, 5 blue marbles, and 3 green marbles. Two marbles are picked at random. What is the fractional probability that 2 red marbles are picked if the first marble was returned before the second was chosen?

Answer 1

Explanation:

Because the first marble was returned before the second was chosen, there are always 4+5+3 = 12 marbles.

Probability of picking 1 red marble = number of red marbles / total number of marbles

= 4/12

= 1/3

Probability of picking 1 red marble two times in a row = Probability of picking 1 red marble * Probability of picking 1 red marble

= 1/3 * 1/3

= 1/9