A complex Engineering system is composed of five subsystems.Each of

these subsystems is independent of the other four. The lifetime, in hours,

of each of these subsystems is given by:

f(x) =0 if x<=100, and f(x)=100/(x^2)

What is the probability that exactly 2 out of the 5 subsystems in this complex system, will have to be replaced within the first 150 hrs. of operation?

Thanks in advance.

x is representing the lifetime of each subsystem.