HELP please will medal
There are
810 dishes that need to be rinsed. Miguel can rinse them in 135 minutes by himself. It will take his friend Ravi 90 minutes to rinse these dishes. How long will it take them if they rinse these 810 dishes together?

Question

HELP please will medal
There are 
810 dishes that need to be rinsed. Miguel can rinse them in 135 minutes by himself. It will take his friend Ravi 90 minutes to rinse these dishes. How long will it take them if they rinse these 810 dishes together?

anonymous · Answer

John`s rate of work = 810 / 135 dishes / min
Bob`s rate of work = 810 / 90 dishes / min

Combined rate = 810/135 + 810/90 dishes / min
Combined rate = 6 + 9 = 15 dishes / min

Time = 810 / 15 min = 54 min