Probability of modules failing

[Elix]

Suppose a system has two modules,

and

, that function independently. Module

fails with probability

and Module

fails with probability

, when the system is executed. When the system is executed, find the probability that:

(a) only Module

fails.

(b) only Module

fails.

(c) both modules fail.

(d) neither module fails.

(e) What do the probabilities add up to?

Ive tried doing a) but cant see the logic behind it

 

[Dr.Peterson]

Please show the work you've done, even if you are sure it's wrong. That will give us a place to start in discussing it.