Multiple choice

A and B can do a piece of work in 20 days while B and C can do the same piece of work in 30 days and C and A can do the same piece of work in 40 days. In how many days can C alone do 30% of that work?

  1. 78

  2. 76

  3. 72

  4. 84
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let A+B, B+C, C+A work rates be 1/20, 1/30, 1/40 respectively per day. Adding all: 2(A+B+C) = 1/20+1/30+1/40 = 13/120. So A+B+C = 13/240 per day. C alone = (13/240) - (1/20) = 13/240-12/240 = 1/240 per day. For 30% work: 0.3×240 = 72 days.

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