math

22. Bob and James are finishing the roof of a house. Working alone, Bob can shingle the roof in 10 hours. James can shingle the same roof in 16 hours. How long will it take them working together to shingle the roof? Round your answer to the nearest hundredth if necessary


I don’t understand this

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  1. look at how much of the job each can do in 1 hour
    Bob does 1/10 of the job
    James does 1/16 of the job.
    Together, they can do 1/10 + 1/16 = 13/80 of the roof in one hour
    So, it will take them 80/13 = 6 2/13 hours

    This is why the solution to such work problems is usually written

    1/10 + 1/16 = 1/x

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    oobleck
  2. 26.67 hours i think

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  3. Wait... no it's 6.15 hours

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