# A certain airplane has two independent alternators to provide electrical power. The probability that a given alternator will fail on a 1-hour flight is .02. What is the probability that one or the other will fail?

##### 1 Answer

Sep 14, 2017

.0396

#### Explanation:

okay, digging back into the depths of my memory of probability & statistics...

the probability that 1 or the other will fail is 1 minus the probability that neither will fail.

Probability that each alternator will NOT fail is .98

Statistically independent events, so, you multiply these together.

1 - (.98 x .98) = .0396

Way, way back when I was young, I entered Navy flight training on the T-28 Trojan.

https://en.wikipedia.org/wiki/North_American_T-28_Trojan

...which had a 1475 horsepower piston engine, with 2 alternators, just as described here, for safety. (They called them "magnetos" instead of alternators, but same thing.)

..because the probability of BOTH of them failing is only .02 x .02 = .0004

Much safer!