Bihar Police Constable Model Paper 4

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.