Multiple choice

A can do piece of work in 12 days and B in 15 days. They worked together for 4 days and then A left. The days taken by B to finish the remaining work is

  1. 4

  2. 5

  3. 6

  4. 8
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A's rate = 1/12, B's rate = 1/15. Together = 1/12 + 1/15 = 9/60 = 3/20. In 4 days, they do 4 * (3/20) = 3/5 of the work. Remaining work = 2/5. B takes (2/5) / (1/15) = 6 days.

AI explanation

Assuming the total work is the least common multiple of 12 and 15, we get 60 units. The daily work rates of A and B are 5 units and 4 units respectively, so working together for 4 days they complete 36 units. This leaves 24 units of work for B to complete alone. Dividing the remaining 24 units by B's daily rate of 4 units gives 6 days. The result is 6 days.

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