Multiple choice

A and B together can dig a pond in 10 days. They worked together for 4 days and then B left the job. In how many days would A complete the job, if he can alone dig the pond in 30 days?

  1. 12 days

  2. 14 days

  3. 18 days

  4. 30 days

  5. 10 days
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A's rate = 1/30. (A+B)'s rate = 1/10. So B's rate = 1/10 - 1/30 = 2/30 = 1/15. They work together for 4 days: 4 * (1/10) = 4/10 = 2/5. Remaining work = 3/5. A completes this in (3/5) / (1/30) = 3/5 * 30 = 18 days.

AI explanation

The combined one-day work of A and B is 1/10, so in 4 days they complete 4/10 or 2/5 of the job. The remaining work is 1 - 2/5 = 3/5 of the job. Since A alone can complete the entire job in 30 days, A will complete the remaining 3/5 of the job in 3/5 * 30 = 18 days.

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