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A copy machine can copy a report in 30 mins. When a second copy machine is used at the same time, the copying can be done in 18 min. How long would it take the second copy machine to do the copying alone?
Nice try, but let's do it this way.
Let x = time required when using both machines.
Let the completed job = 1
we know that copy machine 1 will do x/30 of the job
copy machine 2 will do x/18 of the job
Machine 1's fraction + Machine 2's fraction = the completed job (1)
Get rid of those annoying denominators, multiply equation by 30*18 = 540
Cancel out the denominators and you have:
18x + 30x = 540
48x = 540
x = 11.25 minutes or we could say 11 min 15 secs
Check our solution like this:
11.25/30 + 11.25/18 =
.375 + .625 = 1
Did this make sense to you? Enlighten you a little bit?