2021 · Q53
A and B together can finish a job in 20 days. B and C together can finish the same job in 30 days. If A and C together can finish it in 24 days, in how many days can A alone finish the job?
general-mental-abilityquantitative-aptitude
- A35 2/7 days
- B37 1/7 days
- C34 2/7 days
- D33 2/7 days
Explanation
Let daily work rates be a, b, c. Then a + b = 1/20, b + c = 1/30, c + a = 1/24. Adding all three gives 2(a + b + c) = (6 + 4 + 5)/120 = 15/120 = 1/8, so a + b + c = 1/16. Subtracting (b + c) = 1/30 gives a = 1/16 − 1/30 = 7/240. A alone takes 240/7 = 34 2/7 days. Hence option C is correct.