Multiple choice

Karan can build a wall in 20 days, while Amit can completely destroy the wall in 40 days. Kapil can build the wall twice as efficiently as Karan. If Karan, Kapil and Amit start working at the same time, then in how many days will the wall be completely built?

  1. 6 days

  2. 8 days

  3. 11 days

  4. 15 days

  5. 16 days
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Karan rate = 1/20. Amit rate = -1/40. Kapil rate = 2 * (1/20) = 1/10. Combined rate = 1/20 + 1/10 - 1/40 = (2+4-1)/40 = 5/40 = 1/8. Time = 8 days.

AI explanation

Using the LCM method, let the total work be 40 units. Karan builds 2 units per day and Amit destroys 1 unit per day. Kapil is twice as efficient as Karan, so Kapil builds 4 units per day. Working together, their net building rate is 2 plus 4 minus 1, equaling 5 units per day. The time to completely build the wall is 40 divided by 5, which equals 8 days.

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