Given: Time taken to fill tank by A = 12 hours Time taken to fill tank by B = 16 hours Time taken to empty tank by C = 8 hours Concept used: Total time = (Total volume)/(volume filled/empty in 1 hr) Calculation: Volume filled by A in 1 hr = 1/12 Volume filled by B in 1 hr = 1/16 Volume emptied by C in 1 hr = 1/8 Total volume filled after all pipes are open for 1 hr = 1/12 + 1/16 - 1/8 [The efficiency of outlet pipe is opposite to inlet pipe] ⇒ Required volume in 1 hr = (4 + 3 - 6)/48 ⇒ Required volume filled in 1 hr = 1/48 Total time to fill tank = (Total volume)/(Volume filled in 1 hr) ⇒ Total time = 1/(1/48) ⇒ Total time = 48 hours ∴ The Total time taken to fill the tank is 48 hours.