Given, a tap can fill a tank in 10 hours. ∴ In 1 hour, the tap fills 1∕10th part of the tank. To fill half the tank, time required =5 hours. Now, part of tank empty = 1/2 Given, 4 more similar taps are opened. ∴ In 1 hour, 5 taps fill part of tank =5×1∕10=1∕2 ∴ to fill the half filled tank, the taps require 1 hr . Total time taken =5hr+1hr=6hr