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Posted by on Tuesday, September 28, 2010 at 8:16am.

Andy and William work together to build a toy house. It will take William 5 hours and Andy 4 hours, or William 10 hours and Andy 2 hours to finish their work. If William works alone, how many hours will it take to finish his work?
5
10
15
20

Explain how you arrived at the answer.

  • math word problem - , Tuesday, September 28, 2010 at 10:43am

    There are two ways to do this, as a logic problem or as an algebra problem

    If it will take William 5 hours and Andy 4 hours, or William 10 hours and Andy 2 hours to finish their work, then each decrease in time by Andy of 2 hours results in 5 more hours of work by William. So if Andy's work goes to zero then there will be 5 more hours of work required by William, so
    10h + 5 h = 15 h.

    By algebra if we say that the rate of work by William is x and that by Andy is y then

    5x+4y=T Total task .....1
    10x+2y=T

    or
    20x+4y=2T ..............2

    subtract 1 from 2

    15x=T, so it takes William 15 h

  • math word problem - , Tuesday, September 28, 2010 at 10:55am

    Thank you Dr. Russ. I am so thrilled with your answer. It is the first time I have had an answer that I can truly understand and comprehend, being a math-challenged individual. Thank you sooo much for your careful and complete explanation!

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