Multiple choice

Pipe A can fill a tank in $10h$ and pipe $B$ can fill the same tank in $12h$. Both the pipes are opened to fill the tank and after $3h$ pipe $A$ is closed. Pipe $B$ will fill the remaining part of the tank in

  1. $5h$
  2. $4h$
  3. $5h$ $24min$
  4. $3h$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Work rates: A = 1/10, B = 1/12. In 3 hours, A+B do 3 * (1/10 + 1/12) = 3 * (11/60) = 33/60 = 11/20. Remaining work = 9/20. B takes (9/20) / (1/12) = 9/20 * 12 = 108/20 = 5.4 hours, which is 5 hours 24 minutes.

AI explanation

Using the LCM method, let the total capacity of the tank be 60 units. Pipe A fills at 6 units per hour and pipe B fills at 5 units per hour, so together they fill 11 units per hour. In 3 hours, they fill 33 units, leaving 27 units to be filled by pipe B alone. Dividing 27 units by pipe B's rate of 5 units per hour gives 5.4 hours, which is 5 hours and 24 minutes.

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