Multiple choice

A can do a work in 20 days and B in 50 days. If they work on it together for 5 days, then what fraction of work is left?

  1. 13/20

  2. 1/3

  3. 1/6

  4. 2/9
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A Correct answer
Explanation

A's rate is 1/20 per day, and B's rate is 1/50 per day. Their combined rate is 1/20 + 1/50 = 7/100 per day. In 5 days, they complete 5 * (7/100) = 35/100 = 7/20 of the work. The work left is 1 - 7/20 = 13/20.

AI explanation

Using the LCM method, let the total work be the least common multiple of 20 and 50, which is 100 units. The one-day work of A is 5 units and B is 2 units, making their combined one-day work 7 units. Working together for 5 days, they complete 5 x 7 = 35 units of work. The remaining work is 100 minus 35 = 65 units, so the fraction of work left is 65/100, which simplifies to 13/20.

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