the officejet printer can copy maria'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?

Answer 1

rate1= 1/18
rate2=1/22

combined reate= rate1+rate2=40/18*22

combined rate= 1/9.9 min

so,9.9 min

LEt me show you another neat way.
In in 22*18 min, one machine can do 18, the other 22.

so rate= (18+22)/22*18

dissertations= rate*time
time= 1dissertation/rate= 22*18/40=9.9min