Two pipes A & B can fill a cistern in 16 and 24 minutes respectively. If both the pipes are opened simultaneously, then after how much time should B be closed so that the tank is filled in 12 minutes?
Explanation:
Let B closed after x mins, then part filled by (A + B) in x mins + part filled by A in (12 - x) mins = 1]
∴ x116+124+12-x116=1 or 5x48+12-x16=1
⇒ 5x + 36 - 3x = 48
⇒ 2x = 12 ⇒ x = 6
So, B must be closed after 6 mins.
Hence, option (b).
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