Armco, a manufacturer of traffic light systems, found that under accelerated-life tests, 95 percent of the newly developed systems lasted 3 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 3 years?
b. Which rule of probability does this illustrate?
c. Using letters to represent the four systems, write an equation to show how you arrived at the answer to part (a).