Question

Pipe A can fill an empty tank in 5 hours while pipe B can empty the full tank In 6 hours. If both are opened at the same time in the empty tank, how much time will they take to fill it up completely?

Answer 1

Pipe A's one hour's work for filling the tank$=\frac{1}{5}$

Pipe B's one hour's work for emptying $=\frac{1}{6}$

Both pipes are opened, then

Both's one hour's work $=\frac{1}{5}-\frac{1}{6}$

$=\frac{6-5}{30}=\frac{1}{30}$

$\therefore$ The empty tank will be filed in 30 hours