Multi-processing cpu utilization estimate I find a formula on my book to estimate cpu utilization under multi-processing.

$ U = 1 - P^n $

U: cpu utilization
P: cpu idle

I want to know why or how to proof.

Edit:

The book is about operating system, not in english.

This may be like https://stackoverflow.com/questions/20328619/calculate-cpu-utilization/20328695?noredirect=1#comment88673153_20328695

I get an answer that is 


  it's just basic probability theory
$P^n$ is the probability that all "cores" are idle simultaneously, hence $1-P^n$ is the probability that at least one core is in use.