Multiple choice

If A and B, together, can finish a piece of work in 10 days and B, alone, can finish it in 20 days. In how many days can A alone finish the work?

  1. 21 days

  2. 20 days

  3. 19 days

  4. 24 days
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

If A+B = 1/10 and B = 1/20, then A = 1/10 - 1/20 = 1/20. So A takes 20 days.

AI explanation

Let the total work be the least common multiple of 10 and 20, which is 20 units. The combined efficiency of A and B is 20 divided by 10, or 2 units per day. Since B alone finishes the work in 20 days, B's efficiency is 20 divided by 20, or 1 unit per day. A's efficiency is 2 minus 1, resulting in 1 unit per day, so A alone takes 20 divided by 1 days to finish the work.

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