An urn contains 1 green ball, 1 red ball, 1 yellow ball and 1 white ball. I draw 4 balls with replacement. What is the probability that there is at least one color that is repeated exactly twice?

Probability P (getting exactly 1 colour repeated twice) = 1/128

Step-by-step explanation:

Green ball=1, red ball = 1, Blue ball=1, yellow ball = 1

Assuming the two colours are green balls

P (Green ball) = 1/4

P (green ball) = 1/4

P (blue ball) = 1/4

P (yellow or white) = 2/4

P (getting exactly 1 colour repeated twice) = 1/4 * 1/4 * 1/4 * 2/4 = 2/256 = 1/128