A bag contains 7 green balls and 8 white balls. If two balls are picked at the same time, what is the probability that both balls are of the same color?

Explanation

The number of ways to select two green balls from seven is ⁷C₂, and the number of ways to select two white balls from eight is ⁸C₂. The total number of ways to pick any two balls from the 15 is ¹⁵C₂. Therefore, the probability that both balls are the same color is (⁷C₂ + ⁸C₂) / ¹⁵C₂ = 7/15.