An inlet pipe fills in 6 hours and an outlet pipe emptys in 10; How long to fill both?

Question

An inlet pipe can fill a vat in 6 hours, while the outlet pipe emptys it in 10 hours. How long will it take to fill the vat if both pipes are left open?

Comments

Please Help!!!!

Answer 1

In each hour, the vat will fill 1/6 and drain 1/10.

In common denominators: 5/30 - 3/30 = 2/30 = 1/15.

The vat fills 1/15 per hour, so will be full in 15 hours.