Posted by **Sue** on Saturday, September 12, 2009 at 4:02pm.

The officejet printer can copy Sue's dissertation in 18 min. The laserjet printer can copy the same document in 22 min. If the two machines work together how long would they take to copy the dissertation?

Any help would be greatly appreciated.

- Math -
**bobpursley**, Saturday, September 12, 2009 at 4:07pm
In 18*22min, laserjet can do 22, and the officejet can do 18. So the rate is

rate= number/time= (18+22)/22*18=40/396min = 1dissertation/9.9 min

that answers it, but formally

dissertations= rate*time

time= dissertations/rate= 1dissertation/(1dissertation/9.9min)= 9.9 min

- Math -
**Sue**, Saturday, September 12, 2009 at 4:08pm
Would it be 99/10?

- Math -
**Sue**, Saturday, September 12, 2009 at 4:08pm
Thank you for your help.

- Math -
**bobpursley**, Saturday, September 12, 2009 at 4:09pm
yes, but few folks say 99/10 min, most would say 9.9 minutes, or 9 minutes 54seconds.

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