Multiple choice

A can do a piece of work in 9 days and B in 18 days. They begin together, but A goes away 3 days before the work in finished. The work lasts for

  1. 6 days

  2. 8 days

  3. 12 days

  4. 10 days
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let total days be x. A works for (x-3) days, B works for x days. (x-3)/9 + x/18 = 1. Multiply by 18: 2(x-3) + x = 18, so 2x - 6 + x = 18, 3x = 24, x = 8.

AI explanation

Using the assumption method, let the total work be the least common multiple of 9 and 18, which is 18 units. A completes 2 units per day and B completes 1 unit per day, and since A leaves 3 days before completion, B works alone for the last 3 days to finish 3 units. This leaves 15 units to be completed by A and B working together. Their combined rate is 3 units per day, so they work together for 5 days, making the total time 5 plus 3, which equals 8 days.

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