# I can't remember how to set up this problem

• June 2nd 2010, 05:37 PM
charles2
I can't remember how to set up this problem
A company has installed a generator to back up the power in case there is a power failure. The probability that there will be a power failure during a snowstorm is .35. The probability that the generator will stop working during a snowstorm is .05. Find the probability that during a snowstorm the company will have at least one power source. Of course, the two power sources function independently.

I know I just need to multiply the probability of power failure during a snowstorm and probability the generator will stop working during the snowstorm, but how would I correctly set up the problem?
• June 2nd 2010, 06:16 PM
TKHunny
Ponder this: $(0.35 + 0.65)\cdot (0.05 + 0.95)$

Multiply out to produce all four terms. Think on the meaning of each of the four terms.
• June 2nd 2010, 06:21 PM
charles2
Doesn't that equal 1?

I'm sorry, I don't understand.
• June 2nd 2010, 06:32 PM
TKHunny
Yes, the total it unity. It's supposed to be. That tells us that we haven't missed anything.

Resist the temptation to simplify as you go. Did you write the four terms?

0.35 * 0.05 means what?
0.35 * 0.95 means what?
0.65 * 0.05 means what?
0.65 * 0.95 means what?