Multiple choice

A and B together can do a piece of work in 20 days, whereas B and C together can do the same piece of work in 30 days. How many days will A and C together take to complete the same piece of work?

  1. 10 days

  2. 24 days

  3. 25 days

  4. Cannot be determined
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let A, B, C be the work rates. A + B = 1/20 and B + C = 1/30. We want A + C. Subtracting the equations gives A - C = 1/20 - 1/30 = 1/60. We cannot determine A + C without knowing the individual rates or another relation.

AI explanation

Let A's one day work be 1/x and C's one day work be 1/z, with their combined work being 1/20 for A and B, and 1/30 for B and C. To find the combined work of A and C, the method requires adding the first two equations to get (A+B) + (B+C) = A + C + 2B, which equals 1/20 + 1/30 = 1/12. Since the individual work value of B is not provided, we cannot isolate the combined value of A and C, so the required time cannot be determined.

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