Multiple choice

A can finish a piece of work in 48 days and B can finish it in 60 days. They work together for 12 days and then A goes away. In how much time (in days and hours) will B finish 25% of the remaining work?

  1. 6 days 4 hours

  2. 8 days 8 hours

  3. 6 days 6 hours

  4. 8 days 6 hours
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

A's work rate = 1/48 per day, B's = 1/60 per day. Combined rate = 1/48 + 1/60 = 9/240 = 3/80 per day. In 12 days, they complete 12 × 3/80 = 36/80 = 9/20 of work. Remaining work = 11/20. B must finish 25% of this = (1/4) × (11/20) = 11/80. At B's rate of 1/60 per day, time = (11/80) / (1/60) = (11/80) × 60 = 660/80 = 33/4 = 8.25 days = 8 days 6 hours.

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