John can paint a room in 3 hours. His apprentice, working alone, requires 6 hours to do the same job.

Question

How long would it take John and his apprentice, working together, to paint the room if they continue to work at the given rates?

Answer 1

John's rate = room/3
Apprent's rate = room/6
combined rate = room/2 + room/6
= 3room/6 = room/2

time at combined rate = room/(room/2))
= 1/(1/2) = 2 hours