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Math Help - How many legs?

  1. #1
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    How many legs?

    I had a question in a test the other day, which I couldn't work out. It sounds relatively trivial, but I just couldn't do it.

    It went like this...

    In a farm there are 16 animals which are made up of rabbits and chickens only. We know there are 42 legs altogether.

    How many chickens and rabbits are there?


    This is my version but it took me nowhere...

    chicken = 2 legs
    rabbits = 4 legs

    2X + 4X = 42 so 6X = 42 and X = 7

    So 7 chickens and 7 rabbits... but we need 16 animals altogether???? Need help please.
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  2. #2
    MHF Contributor Also sprach Zarathustra's Avatar
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    There two variables x and y.

    The equations are:

    (1) 2x+4y=42
    (2) x+y=16
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  3. #3
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    ahhhh yes.

    so y = 5 and x = 11
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  4. #4
    MHF Contributor Also sprach Zarathustra's Avatar
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    Yes!

    11 chickens and 5 rabbits.
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  5. #5
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    Thank you!
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  6. #6
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    Quote Originally Posted by Natasha1 View Post
    I had a question in a test the other day, which I couldn't work out. It sounds relatively trivial, but I just couldn't do it.

    It went like this...

    In a farm there are 16 animals which are made up of rabbits and chickens only. We know there are 42 legs altogether.

    How many chickens and rabbits are there?


    This is my version but it took me nowhere...

    chicken = 2 legs
    rabbits = 4 legs

    2X + 4X = 42 so 6X = 42 and X = 7

    So 7 chickens and 7 rabbits... but we need 16 animals altogether???? Need help please.
    When you write 2X+4X=42,

    you are inadvertently exclaiming that the number of rabbits equals the number of chickens
    (if both numbers is X).

    Remember, 2 unknowns is solved with 2 clues (equations),
    3 unknowns is solved with 3 seperate clues,
    1 unknown only requires 1 clue etc.
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  7. #7
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    Yes yes. I have noticed my mistake now. Thanks
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