Multiple choice

A, B and C together can complete a work in 15 days. B and C can complete the same work in 20 days. In how many days can A alone complete the same work?

  1. 40

  2. 45

  3. 60

  4. 75
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Rate of (A+B+C) = 1/15. Rate of (B+C) = 1/20. Rate of A = 1/15 - 1/20 = (4-3)/60 = 1/60. A takes 60 days.

AI explanation

Using the LCM method, let the total work be the least common multiple of 15 and 20, which is 60 units. The combined efficiency of A, B, and C is 60/15 = 4 units per day. The efficiency of B and C together is 60/20 = 3 units per day. The efficiency of A alone is 4 minus 3, which equals 1 unit per day. Therefore, A alone can complete the 60 units of work in 60 days.

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