Question

Pipe a can fill a tank three times faster than pipe b. If together a and b can fill the tank in 40 minutes, then b alone will be able to fill the tank in:

Answer 1

Let the volume of the tank be y
Let the speed at which pipe b fills be x.
So speed of pipe a will be 3x.

Total speed is 4x.

y/4x = 40
y = 160x

Now b is alone, so the total speed is x.

y/x = z
y = zx

Now equating the RHS of both the equation :
160x = zx
z = 160 mins