Multiple choice

20 boys can complete a piece of work in 25 days and 25 girls can complete the same work in 22 days. If all the 20 boys and 25 girls work together, then in approximately how many days will the work be completed?

  1. 11 days

  2. 10 days

  3. 15 days

  4. 12 days

  5. None of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Boy's rate = 1/(20*25) = 1/500 work/day. Girl's rate = 1/(25*22) = 1/550 work/day. Combined rate = 20*(1/500) + 25*(1/550) = 20/500 + 25/550 = 1/25 + 1/22 = (22+25)/550 = 47/550. Time = 550/47 = 11.7 days, which is approximately 12 days.

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