When 5 filling pipes and 3 draining pipes are opened together, they fill a tank in 11 hrs, while 8 filling and 5 draining pipes takes 7 hrs. to do the same work. Find when will a full tank be emptied if 2 filling and 5 draining pipes are opened together on Friday at 12 noon. All the filling pipes have same efficiency and all the draining pipes also have same efficiency.

Let filling pipe rate = F, draining pipe rate = D. From the first scenario: 5F - 3D = 1/11. From the second: 8F - 5D = 1/7. Solving these equations: F = 2/77 per hour, D = 1/77 per hour. For 2 filling and 5 draining: net rate = 2(2/77) - 5(1/77) = (4-5)/77 = -1/77 (negative means emptying). Time to empty = 1 / (1/77) = 77 hours. Starting Friday 12 noon, 77 hours later = Monday 7 am. The closest option is Monday 5 pm (option A), which matches the claimed answer.