Question 393524
1) Find the hourly rate of computer A.
2) Find the hourly rate of computer B.
3) Add these to get the hourly rate of both computers working together.
4) Invert this number to get the time to complete the job working together.
If A can do the job in 4 hours, then it can do {{{1/4}}} of the job in 1 hour.
If B can do the job in 2 hours, then it can do {{{1/2}}} of the job in 1 hour.
Together, they can do {{{1/4+1/2 = 3/4}}} of the job in 1 hour.
So, together, they can do the whole job in {{{4/3 = 1}}}{{{1/3}}} hours, or 1 hour and 20 minutes.