multithreading - duration of jobs " How long will it take for 2 jobs to complete if they're running in parallel, knowing that both have a total of 20 minutes of CPU usage time and 50% IO"

I calculated the CPU usage: 1-0.5²=75%.
To my understanding, if they're running sequentially, time needed to completion is 80 minutes (each job needs 40 minutes to complete)
therefore time needed to complete both jobs in parallel is 75% * 80 = 60 minutes.

However here is the correct answer: 

" CPU utilization is 75%. Thus each one gets 0.375 CPU minute per real time minute. To accumulate 20 minutes of CPU time, a job must run 20/0.375=53.33 minutes. Thus, in parallel, time to completion for both jobs is 53.33 minutes".

I don't get where the 0.375 came from ?

What are CPU minutes ?

Help is appreciated
I don't get where the 0.375 came from ?


If the CPU utilization is 75%, and it's shared equally between two process, each of them gets 37.5%.


  What are CPU minutes?


A CPU-minute is the amount of work done by one CPU in one minute.