Question

the officejet printer can copy lisa's dissertation in 18 min. the laserjet printer can copy the same document in 20 min. if the two machines work together, how long would the take to copy the dissertation
PsyDAG
If each was given half of the dissertation, wouldn't it be 19 minutes?
nono
Wouln't it have to be a shorter timeframe since they are both working together? and one of them does it in 18 mins ..