A tap can fill an empty tank in 12 h and a leakage can empty

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A tap can fill an empty tank in 12 h and a leakage can empty the tank in 20 h. If tap and leakage both work together, then how long will it take to fill the tank?

1. 25 h
2. 40 h
3. 30 h
4. 35 h

Correct Option: C

Part filled by tap in 1 h = 1/12
Part emptied by leak in 1 h = 1/20
Net part filled in 1 h when both (tap and leakage) work = 1/12 - 1/20
= (5 - 3)/60 = 2/60 = 1/30

∴ Required time to fill the tank = 30 h