Question

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?

Answer 1

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.