3563. In the urn there are 7 balls with numbers from 1 to 7. At random, one by one remove two balls without return. Find the probabilities of the following events: a) balls with numbers 1,4 will appear successively; b) the extracted balls will have numbers 1.4, regardless of the sequence in which they appeared.

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