what is the probability ????

Armco, a manufacturer of traffic light systems, found that under quality tests, 95% of the newly developed systems lasted at least three years before failing to change signals properly.

a. If a city purchased four of these systems, what is the probability all four systems would operate properly for at least three years?

b. Which rule of probability does this illustrate? Explain.

2. a. In how many ways can a committe of two members be selected from a group of 12 candidates?

b. In how many ways can a chairperson and vice-chairperson be selected from a group of 12 candidates?