RRB Paramedical Staff Nurse Model Paper 1

There are two auto closed pipes X and Y which get closed if there is any disturbance can fill a tank in 10 and 15 hrs. respectively. Both the pipes are opened to fill the tank but when the tank is 1/3 rd full, a leak develops in the tank which results in closing of both pipes. Through the leak one-third water supplied by both the pipes goes out & after it the leak was get closed by some means and both filling pipes again start filling the tank. The total time taken to fill the tank is