Решение задачи N1897 теория вероятностей Бернулли

1897. The packer places 9 instruments, checked by the OTC or manufactured by workers who have a personal stamp. The probability that the device is marked with a personal brand is 0.25. What is the probability that the devices marked OTC will be: a) at least two; b) exactly two?

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