Two pipes A and B can fill a tank in 10 hrs and 40 hrs respectively. If both the pipes are opened simultaneously, how much time will be taken to fill the tank?
8 hours
6 hours
4 hours
2 hours
Explanation:
Pipe A can fill $\dfrac{1}{10}$ of the tank in 1 hr
Pipe B can fill $\dfrac{1}{40}$ of the tank in 1 hr
Pipe A and B together can fill $\dfrac{1}{10}+\dfrac{1}{40}=\dfrac{1}{8}$ of the tank in 1 hr
i.e., Pipe A and B together can fill the tank in 8 hours