Multiple choice

Two pipes A and B can fill a tank in $24$ and $30$ minutes respectively. Both are turned on together. But at the end of $8$ minutes, the first is turned off. The time taken to fill the tank B is

  1. $10\ min.$
  2. $8\ min.$
  3. $12\ min.$
  4. $16\ min.$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Pipe A fills 1/24 per min, B fills 1/30 per min. In 8 mins, A and B fill 8 * (1/24 + 1/30) = 8 * (5/120 + 4/120) = 8 * 9/120 = 72/120 = 3/5. Remaining tank = 2/5. Pipe B fills 2/5 at 1/30 rate: (2/5) / (1/30) = 12 minutes.

AI explanation

Let the total tank capacity be 120 units, making the rates for pipe A 5 units per minute and pipe B 4 units per minute. Working together for 8 minutes, they fill 9 units per minute multiplied by 8, totaling 72 units. The remaining 48 units are filled by pipe B alone at 4 units per minute, which takes 12 minutes.

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