The first pipes passes by 15 liters of water per minute less than the second pipe.

The first pipes passes by 15 liters of water per minute less than the second pipe. How many liters of water per minute passes the first pipe if the tank of 100 liters is fills for 6 minutes longer than the second pipe?

Denote the filling speed of the first pipe as x l / min.

In this case, the filling speed of the second pipe will be: x + 15 l / min.

We obtain the difference equation time filling the pool.

100 / x – 100 / (x + 15) = 6.

We are freed from denominator.

100 * x + 1500 – 100 * x = 6 * x ^ 2 + 90 * x.

We get a square equation.

6 * x ^ 2 + 90 – 1500 = 0.

x ^ 2 + 15 * x – 250 = 0.

D ^ 2 = 15 ^ 2 – 4 * 1 * (-250) = 225 + 1000 = 1225.

D = 35.

x = (-15 + 35) / 2 = 20/2 = 10 l / min.

Answer: The first pipe passes 10 l / min.