math
posted by dan .
There are two machines that produce aluminum cans. The newer machine can produce 7200 cans in 200 minutes. It takes the older machine 300 minutes to produce that many cans. If the two machines work together, how long will it take them to produce 7200 cans?
i did
200x+300x = 7200
500x=7200
x=14.4mins?

rate of newer machine =7200/200 can/min
= 36 cans/min
rate of older machine = 7200/300 cans/min
= 24 cans/min
so combined rate = 36+24 = 60 cans/min
so time for combined work = 7200/60 = 120 minutes.