Question

Working alone at its constant rate pump x pumped out 1/4 of the water in a tank

Answer 1

Pump X took 4 hours to pump out half of the volume.. Let the total volume be V

in 1 hour .. Pump X will pump V/8 water

If pump X and Y both take 3 hours together to pump out the remaining V/2 water.. this means.. For 3 hours Pump X has also been pumping water along with Y.

Water pumped by Y in 3 Hours = V/2-3V/8=V/8 (remaining volume- volume removed by pump X in 3 hours)

this means.. Pump Y takes 3 hours to pump out V/8 water

in 1 hour.. Pump Y can pump V/24 Water...(This is the Rate of pumping of Pump Y)

therefore in order to pump out V water..

pump Y will take V/V/24 = 24 hours :)