Multiple choice

Kishan takes 24 days to build a building while Neeraj takes 9 days to destroy it completely. If Kishan works for 12 days and then, Neeraj joins him and works for another 6 days only, then in how many days will Kishan alone build the remaining building?

  1. 18 days

  2. 21 days

  3. 22 days

  4. 24 days

  5. 25 days
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Kishan's rate is 1/24 per day. Neeraj's rate is -1/9 per day. In 12 days, Kishan does 12/24 = 1/2 work. Then they work together for 6 days: 6 * (1/24 - 1/9) = 6 * (3/72 - 8/72) = 6 * (-5/72) = -5/12. Total work done = 1/2 - 5/12 = 1/12. Remaining work = 11/12. Kishan finishes this in (11/12) / (1/24) = 22 days.

AI explanation

Let the total work be 72 units, making Kishan's efficiency 3 units per day and Neeraj's efficiency negative 8 units per day. Kishan works for 12 days to complete 36 units, and then they work together for 6 days with a combined efficiency of negative 5 units per day, destroying 30 units. The net work completed after these 18 days is 6 units, leaving 66 units of work remaining for Kishan to finish alone. Kishan will complete the remaining building in 66 units divided by 3 units per day, which equals 22 days.

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