Question 10
A cistern is connected with three inlet pipes A, B and C. Pipe A can fill the tank in 4 hours, pipe B in 8 hours, and C in 10 hours. All the pipes are opened simultaneously at initia. After $X$ hours, A and B closed and remaining tank is filled by pipe C alone. Find the value of $X$ if the total time taken to fill tank is 2 hours 30 minutes.