Question

High speed copier works three times as fast as a regular copier.
When both copiers are used, they can copy a group of documents in 12 minutes.
How long would each copier require to do the copying alone

Answer 1

let T be the time for the reg copier to make one document, and T/3 the time for the HSpeed.

task= rate*time=
group= (group/T + 3group/T)*12

1/12= 4/T
T=48min
T/3=16min