### Shortcut of Pipes and Cisterns

Shortcut 73: One pipe fills and another empties [latex]\frac{AB}{-A+B}[/latex] Question: Pipe A can fill a tank in 4 hours and pipe B can empty the tank in 5 hours. If both pipes are opened together, how long will they take to fill a complete tank? Answer: A = 4 B = 5 Substitute the values