Multiple choice

A is thrice as productive as C. Together they can complete a job in 22.5 days. If B joins them after they have worked for 15 days, then in how many days can they finish the rest of the job, given that B alone can do the job in 15 days?

  1. 6

  2. 3

  3. 9

  4. 2
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A = 3C. (A+C) = 4C. Together they finish in 22.5 days, so total work = 4C * 22.5 = 90C. B does job in 15 days, so B = 6C. After 15 days, A+C have done (4C * 15) = 60C. Remaining work = 30C. A, B, C work together at rate 3C + 6C + C = 10C. Time = 30C / 10C = 3 days.

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