Two pipes are working together to fill a reservoir in 12 hours. The faster pipe fills the reservoir 10 hours quicker than the slower one. How long does the faster pipe take to fill the reservoir on its own?

Explanation

Let the time taken by the faster pipe be x hours. Then, the slower pipe takes x + 10 hours. Working together, their combined rate is 1/12 of the reservoir per hour. So, 1/x + 1/(x + 10) = 1/12. Solving this equation gives x = 20 hours.