Question

Kiyoshi can paint a certain fence in 3 hours by himself. If Red helps, the job takes only 2 hours. How long would it take Red to paint the fence by himself ?

Answer 1

Since Kiyoshi can pain a fence in 3 hours by himself, in another perspective, in 1 hour's time he can paint 1/3 of the fence. When Red helps, both person took only 2 hours. From the 1st statement, we can deduce that Kiyoshi, in 2 hours time will paint 2/3 of the fence. This shows that the remaining 1/3 of the fence was painted by Red in a duration of 2 hours. Since Red brushes 1/6 of the fence in an hour's time. It would take Red 6 hours to pain the fence by himself.