Multiple choice

If one man or two women or four boys or five girls can finish a work in 39 days, then how many days will one man, one woman, one boy and one girl together take to finish the same work?

  1. 40

  2. 10

  3. 30

  4. 20
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Work rates: 1 man = 39 days (1/39 work per day), 1 woman = 78 days (1/78), 1 boy = 156 days (1/156), 1 girl = 195 days (1/195). Combined rate = 1/39 + 1/78 + 1/156 + 1/195 = 20/780 + 10/780 + 5/780 + 4/780 = 39/780 = 1/20. Therefore, working together they complete the work in 20 days.

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