Assume an office has two telephones (A and B) with separate lines and different telephone numbers. The probability that telephone A rings when the office is closed is .30. The probability that telephone B rings when the office is closed is .20

What is the probability that neither telephone rings when the office is closed

2 answers

That neither ring

Probability that A does not ring is .7

Probability that B does not ring is .8

Multiply the two.
If the events are independent, the probability of both/all events occurring is determined by multiplying the probabilities of the individual events.