Single correct option
A and B together can complete a job in 12 days, B and C together in 15 days, and A and C together in 20 days. In how many days can A alone complete the job?
- A. 24
- B. 30
- C. 40
- D. 20
Show answer and solution
Answer: (B) 30
Add the three pair-rates: 2(A + B + C) = 1/12 + 1/15 + 1/20 = (5 + 4 + 3)/60 = 12/60 = 1/5.
So A + B + C = 1/10 per day.
A = (A + B + C) − (B + C) = 1/10 − 1/15 = 1/30.
A alone takes 30 days. (C alone would take 60 days and B alone 20 days — hence the distractor 20.)
So A + B + C = 1/10 per day.
A = (A + B + C) − (B + C) = 1/10 − 1/15 = 1/30.
A alone takes 30 days. (C alone would take 60 days and B alone 20 days — hence the distractor 20.)
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