Решение задачи N1634 теория вероятностей

1634. Two boxes contain 15 pieces each, in the first 10, and in the second 12 standard parts. A detail was taken from the first drawer and moved to the second. Find the probability that at random, the item extracted from the second box will be standard.

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