Решение задачи N4381 теория вероятностей

4381. The box contains three black and four white billiard balls. Two balls are taken out of it at random. What is the probability that:
1) both balls turn out to be black;
2) both balls turn out to be white;
3) will the balls be of different colors?

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