Multiple choice

A, B and C can complete a work in (x), 30 and 45 days, respectively. B and C worked together for 6 days. The remaining work was completed by A alone in 12 days. The value of (x) is:

  1. 24

  2. 20

  3. 18

  4. 15
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Work rates: A = 1/x, B = 1/30, C = 1/45 work per day. B and C together: 1/30 + 1/45 = 5/90 = 1/18 per day. In 6 days, B+C complete 6/18 = 1/3 of work. Remaining 2/3 is done by A in 12 days, so A's rate = (2/3)/12 = 1/18. Since A = 1/x, we have 1/x = 1/18, so x = 18 days.

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