If a pipe A can empty a full tank in x hours and two pipes C & D can fill the tank in y hours and z hours respectively then the part of tank filled in 1 hour, when all the pipes are opened together, is _________.

$\frac{xy+xy-yz}{xyz}$

The correct answer is Option (1) → $\frac{xy+xy-yz}{xyz}$

Pipe A → Work Done = $\frac{-1}{x}$  [Emptying]

Pipe B → Work Done = $\frac{1}{y}$

Pipe C → Work Done = $\frac{1}{z}$

Total work done in 1 hour = $\frac{-1}{x}+\frac{1}{y}+\frac{1}{z}$