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mikaela19900630 Group Title

Mary takes three hours to mow the yard. It takes Sally five hours. How long would it take with them mowing it together? Can someone help me work my way to the answer please? thanks

  • one year ago
  • one year ago

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  1. LogicalApple Group Title
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    A comprehensive approach would be to determine the rate at which Mary mows the yard and the rate at which Sally mows the yard. Then add up the two rates. Based on the information, at what rate does Mary mow a yard ?

    • one year ago
  2. mathdude69 Group Title
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    Think of both of them in terms of how much they get done in an hour. Mary mows 1/3rd of the lawn in an hour Sally mows 1/5th of the lawn in an hour How much of the lawn can they mow together in an hour? How many times must they do that to mow the entire lawn?

    • one year ago
  3. mikaela19900630 Group Title
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    so i would ad the 1/3 and 1/5 together??

    • one year ago
  4. mikaela19900630 Group Title
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    @blondie16

    • one year ago
  5. LogicalApple Group Title
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    If you add up the two rates you get a combined rate in "yards per hour". Swap the fraction to get "hours per yard".

    • one year ago
  6. mikaela19900630 Group Title
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    wait so i would do 3/1 +5/1 ??

    • one year ago
  7. LogicalApple Group Title
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    What did you get for the two rates? @mathdude69 told you what they were, so you just have to add them up :)

    • one year ago
  8. mikaela19900630 Group Title
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    so 8/2?

    • one year ago
  9. LogicalApple Group Title
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    Let's see . . . Mary's rate is 1/3 yard per hour Sally's rate is 1/5 yard per hour So their combined rate is: 1/3 + 1/5 = 8/15 The combined rate they both mow a lawn is 8/15 yard per hour Or, equivalently, 15/8 hours per yard = 1.875 hours per yard.

    • one year ago
  10. mikaela19900630 Group Title
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    wait how doe we get the 15?

    • one year ago
  11. LogicalApple Group Title
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    Because 1/3 + 1/5 is 8/15. You cannot add fractions unless they have a common denominator. \[\frac{ 1 }{ 3 } = \frac{ 5 }{ 15 }\] \[\frac{ 1 }{ 5 } = \frac{ 3 }{ 15 }\] \[\frac{ 1 }{ 3} + \frac{ 1 }{ 5 } = \frac{ 5 }{ 15 } + \frac{ 3 }{ 15 } = \frac{ 8 }{ 15 }\]

    • one year ago
  12. mikaela19900630 Group Title
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    oh okay thank you

    • one year ago
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