A cistern can be filled by a tap in 3 hours while it can be emptied by another tap in 8 hours. If both the taps are opened simultaneously, then after how much time will the cistern get filled?
4.8 hr
2.4 hr
3.6 hr
1.8 hr
Explanation:
Part filled by first tap in 1 hour =$\dfrac{1}{3}$
Part emptied by second tap 1 hour $=\dfrac{1}{8}$
Net part filled by both these taps in 1 hour
=$\dfrac{1}{3}-\dfrac{1}{8}=\dfrac{5}{24}$
i.e, the cistern gets filled in $\dfrac{24}{5}$hours =4.8 hours.