A cistern can be filled by one tap in 4 hours and by another in 3 hours. How long will it take to fill it if both taps are opened together?

Explanation

We have,
Time taken by the first tap to fill the cistern =`4`hours.
Time taken by the second tap to fill the cistern ='3' hours
Work done by the first tap in 1 hour = `1/4`
Work done by the second tap in 1 hour = `1/3`
Thus, work done by both the taps in 1 hour =`1/4 + 1/3`
=`7/12`
Both the taps together will fill the cistern in `12/7` hours.