Решение задачи N4515 теория вероятностей

4515. There are 9 red 6 yellow balls in the urn.
a) two balls are taken out of the urn at the same time. Find the probability that they are the same color.
b) one ball is taken out of the urn at random. What is the probability that the ball is yellow?

Detailed solution. Decorated in Microsoft Word 2003 (Quest decided to use the formula editor)