Question 188603
Let x=amount of time it will take you and Mike to finish
Mike works at the rate of 1/40 computer per min

You work at the rate of 1/60 computer per min

Together you and Mike work at the rate of 1/40 +1/60=3/120 + 2/120=5/120=1/24 computer per min

Before you start, Mike as already assembled (1/40)*20=1/2 of the computer, leaving 1/2 of the computer yet to be done.  So the question is how long will it take you and Mike working together to do the remaining half of the computer

Now our equation to solve is:
(1/24)*x=1/2 (1/2 of the computer, that is) Multiply each side by 24
x=12 min------------------amount of time it will take you and Mike to finish


CK
(1/24)*12=1/2
1/2=1/2

Hope this helps---ptaylor