Multiple choice

If A does a job in 12 days he requests B and C to help him in doing the job so that the job is completed in less time. But B and C are 60% more and 60% less efficient than A respectively. Then in how many days they all will complete the job working together?

  1. 3 days

  2. 4 days

  3. 2 days

  4. 5 days

  5. 7.5 days
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A completes 1/12 of job per day. B is 60% more efficient, so B does 1.6 × (1/12) = 2/15 per day. C is 60% less efficient, so C does 0.4 × (1/12) = 1/30 per day. Together they do 1/12 + 2/15 + 1/30 = 5/60 + 8/60 + 2/60 = 15/60 = 1/4 per day. Time = 1 ÷ 1/4 = 4 days.

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