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-   -   How many boys are there? (https://www.askmehelpdesk.com/showthread.php?t=511285)

  • Sep 27, 2010, 07:04 AM
    hello1kitty
    How many boys are there?
    A math teacher saw a playground full of boys and dogs. He counted 30 heads and 100 legs, how many of them are boys?
  • Sep 27, 2010, 07:17 AM
    Unknown008

    Set up an equation and define some variables.

    Let b be the number of boys.
    Let d be the number of dogs.

    Each dog and each boy has one head, and they add up to 30.

    So, b + d = 30

    Each boy has 2 legs and each dog has 4 legs, for a total of 100 legs (the teacher really counted all of them? :p)

    This gives:

    2b + 4d = 100

    You have now two equations, and two unknowns. Can you now solve the problem? :)

    Post what you get! :)
  • Sep 27, 2010, 07:34 AM
    hello1kitty

    so 15 + 15 = 30

    2(15) + 4(15) = 100

    So there were 15 boys

    Is this correct?
  • Sep 27, 2010, 07:35 AM
    Unknown008

    Not quite...

    2(15) + 4(15) = 30 + 60 = 90

    Try again :)

    Do you know how to use substitution or elimination to solve simultaneous equations?
  • Sep 27, 2010, 08:01 AM
    hello1kitty

    Somewhat, I've never been a big fan of these.

    I will post my answer as soon.
  • Sep 27, 2010, 08:01 AM
    Unknown008

    Ok, I'll be waiting for you :)

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