Решение задачи N1778 теория вероятностей

1778. The buyer purchased a vacuum cleaner and polisher. The probability that the vacuum cleaner will not fail during the warranty period is 0.95, for a polisher this probability is 0.9. Find the probability that
a) both devices will withstand the warranty period;
b) at least one will withstand the warranty period.

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