Multiple choice

A can do one part of the work alone in 20 days while B takes 16 days to do it himself. It takes 8 days for C to work together with A and B. If C and D can work in 60 days, then how many days will D need to complete the work by himself?

  1. 252

  2. 225

  3. 240

  4. 270
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Rates: A=1/20, B=1/16, so A+B=9/80. Since A+B+C=1/8, we get C=1/8-9/80=1/80. Given C+D=1/60, so D=1/60-1/80=1/240. D needs 240 days alone.

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