Let A be the rate of the faster pipe and B be the rate of the slower pipe.

We have A − B = 50 and A + B = 330.

Solving these simultaneous equations, we have:

A − B = 50

A + B = 330

2A = 380

So A = 190. Since B is 50 L/min slower, then B = 140.

CHECK:

190 + 140 = 330

190 − 50 = 140.

So the drainage rate of the faster pipe is 190 L/min and the rate of the slower pipe is 140 L/min.