Multiple choice

A can complete a piece of work in 20 days and B can do the same in 30 days. They work together for 8 days and then A leaves the work. How many days will B take if he has to complete the pending work alone?

  1. 10 days

  2. 20 days

  3. 40 days

  4. 60 days

  5. 90 days
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A's rate = 1/20, B's rate = 1/30. Combined rate = 1/20 + 1/30 = 5/60 = 1/12. In 8 days, they finish 8/12 = 2/3 of the work. Remaining work = 1/3. B takes (1/3) / (1/30) = 10 days.

AI explanation

The Least Common Multiple of 20 and 30 is 60, which represents the total work in units. A completes 60 / 20 = 3 units per day and B completes 60 / 30 = 2 units per day. Together they complete 5 units per day, so in 8 days they finish 8 * 5 = 40 units. The remaining pending work is 60 - 40 = 20 units. Working alone at 2 units per day, B takes 20 / 2 = 10 days to complete the pending work.

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