Question 203045

Let x=amount of time it takes five people to finish one job, then
3x=amount of time it takes five people to finish 3 such jobs
ok.  Three people work at the rate of 1/20 of the job per hour, so one person works at the rate of (1/20)/3 or 1/60 of the job per hour

Five people work at the rate of 5*(1/60) or 5/60 of the job per hour
So, our equation to solve is:
(5/60)*x=1 (1 job, that is)
5x=60
x=12 hours--------------amount of time it takes five people to complete 1 job
3x=3*12=36 hours ------------amount of time it takes five people to complete three such jobs

Another way to look at this problem:

If three persons can complete the job in 20 hours, then the job requires 3*20 or 60 person-hours to complete.  Three such jobs would require 3*60 or 180 person-hours to complete

So, five persons could complete three such jobs in 180/5=36 hours 

Hope this helps----ptaylor