Multiple choice

A and B can do a piece of work in 12 and 18 days respectively. They work together for 4 days, after which A leaves. How many more days will B take to finish the remaining work?

  1. 6 days

  2. 7 days

  3. 8 days

  4. 9 days
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A's work rate = 1/12, B's = 1/18. Combined rate = 1/12 + 1/18 = 5/36. Work done in 4 days = 4 * 5/36 = 20/36 = 5/9. Remaining work = 4/9. B's time to finish = (4/9) / (1/18) = (4/9) * 18 = 8 days.

AI explanation

The one day work method gives A's rate as 1/12 and B's rate as 1/18, so their combined rate is 1/12 plus 1/18, which equals 5/36. In 4 days, they complete 4 times 5/36, which is 20/36 or 5/9 of the work, leaving 4/9 of the work remaining. B alone works at a rate of 1/18 per day, so to finish the remaining 4/9 of the work, B requires (4/9) divided by (1/18) days. This evaluates to (4/9) times 18, which equals 8 days.

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