SOLUTION: An office has an old copying machine and a new one. Working together it takes both machines 4 hours to make all of the copies of the annual financial report. Working alone it takes

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Question 348386: An office has an old copying machine and a new one. Working together it takes both machines 4 hours to make all of the copies of the annual financial report. Working alone it takes the old copying machine 15 hours longer than the new one to make all of the copies. How long would it take the new copying machine to make all the copies alone?
Answer by checkley77(12844) About Me  (Show Source):
You can put this solution on YOUR website!
1/4=1/(X+15)+1/X
1/4=(X+X+15)/X(X+15)
1/4=(2X+15)/(X^2+15X) CROSS MULTIPLY.
X^2+15X=4(2X+15)
X^2+15X=8X+60
X^2+15X-8X-60=0
X^2+7X-60=0
(X+12)(X-5)=0
X-5=0
X=5 HOURS FOR THE NEW MACHINE.
15+5=20 HOURS FOR THE OLD MACHINE.
PROOF:
1/4=1/20+1/5
1/4=(1+4)/20)
1/4=5/20
1/4=1/4