Amachine works for an exponentially distributed time with rate μ and then fails. a repair crew checks the machine at times distributed according to a poisson process with rate λ; if the machine is found to have failed, then it is immediately replaced. find the expected time between replacements of machines.

the order for strong to weak forces such as

strong nuclear force → electromegnetic force → weak nuclear force → gravitational force

the fundamental forces are those forces that act between to objects or element to make interactions. there are four types of fundamental forces such as strong and weak nuclear forces (due to protons and electrons), electromagnetic force (due to the motion of electrons) and gravitational force (due to orbital movement of the planet). if these forces are arranged on the basis of their maximum strength then the order is

strong nuclear force → electromegnetic force → weak nuclear force → gravitational force