A and B together can complete a work in 15 days. B and C together can complete the same work in 20 days. C and A together can do it in 30 days. In how many days can A alone complete the job?
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e. 40 days.
Total work = LCM of (15, 20, 30) = 60
(A + B) = 60 ÷ 15 = 4 units/day
(B + C) = 60 ÷ 20 = 3 units/day
(C + A) = 60 ÷ 30 = 2 units/day
⇒ A = (A + B + C) - (B + C) = (9/2) - 3 = 3/2
Time = Total work ÷ efficiency
A's Time = 60 ÷ (3/2) =120 ÷ 3 = 40 days