1. 20 textbooks are randomly arranged on a library shelf, 6 of them are bound. The librarian takes 3 textbooks at random. Find the probability that at least two textbooks will be bound.
2. The probability that the lamp will remain operational after 1000 hours of operation is 0.5. Find the probability that out of 6 lamps 4 will remain operational after 1000 hours of operation.
3.p_1=0.9,q_1=0.1 p_2=0.8 ,q_2=0.2,p_3=0.7,q_3=0.3
The law of distribution of a random variable - the number of devices activated during an accident.