Correct Answer - Option 2 : 1/60
Calculation:
Pipe A's 1 hour's work = 1/20
Pipe B's 1 hour's work = 1/30
Let leakage 1 hour's work be 1/m.
Pipe(A + B)'s 1 hour's work = 1/20 + 1/30 = 1/12
(Pipe A + pipe B + leakage)'s 1 hour's work = 1/20 + 1/30 - 1/m
⇒ 1/(12 + 3) = 1/20 + 1/30 - 1/m
⇒ 1/m = 1/60
∴ Fraction of tank emptied by a leakage in 1 hour = 1/60