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Answer: Option CExplanation:
Let the cistern be filled by pipe A alone in x hours.
Then, pipe B will fill it in (x + 6) hours.
.'. 1/x + 1/(x + 6) = 1/4
=> (x + 6 + x)/x(x + 6)= 1/4
=> x^2 - 2x - 24 = 0.
=> (x -6)(x + 4) = 0.
=> x = 6. [neglecting the negative value of x]
Answer: Option AExplanation:
Part filled by A in 1 min = 1/20
Part filled by B in 1 min = 1/30.
Part filled by (A + B) in 1 min = 1/20 + 1/30 = 1/12.
therefore, Both pipes can fill the tank in 12 minutes.