Two taps A and B can fill an overhead tank in 10 hours and 15 hours respectively. Both the taps are opened for 4 hours and then B is turned off. How much time will A take to fill the remaining tank?

Explanation

Time taken by A to fill a tank = `10` hours
Quantity of tank filled by A in 1 hour =`1/10` units.
Similarly, Quantity of tank filled by B in 1 hour =`1/15` units.
Now, Quantity of tank filled by A and B together, in 1 hour = units `1/10+1/15=1/6` units.
Hence, Quantity of tank filled by A and B together, in `4 `hours = `4 xx 1/6= 2/3` units.
Quantity of tank left to be filled = `1- 2/3 =1/3` units.
Therefore, time taken by A to fill `1/3` units of tank=`1/3*(10)`
`3 1/3 `hours.