Solution of problem N4381 probability theory

Solution of problem N4381 probability theory

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?

Additional information:

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