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Math Help - Rings Question

  1. #1
    Junior Member mathbuoy's Avatar
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    Exclamation Rings Question

    Please help me with this question. I totally have no idea why the options have decimals Thank you

    Last edited by mathbuoy; May 7th 2011 at 10:55 AM.
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  2. #2
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    Notice that when the chain hangs vertically, the rings are alternately in one of two planes, either in the same plane as the top ring or in a perpendicular plane. If the chain has an odd number of rings in it, then the bottom ring will have a whole number of 180 twists. But if the chain has an even number of rings then the bottom ring must have an additional half-twist.
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  3. #3
    Junior Member mathbuoy's Avatar
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    Thank you explaining!!

    Is my reasoning below right?
    if it's two rings, the bottom ring makes .5 twist.
    if there're 3 rings, the bottom ring makes .5 + .5 twist.
    if there're 6 rings, it should be 2.5 twist.

    The answer is B(.5, 1.5, 2.5) but i don't understand why it's given as .5, 1.5 and 2.5 and not just 2.5 twist.
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  4. #4
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    Quote Originally Posted by mathbuoy View Post
    Thank you explaining!!

    Is my reasoning below right?
    if it's two rings, the bottom ring makes .5 twist.
    if there're 3 rings, the bottom ring makes .5 + .5 twist.
    if there're 6 rings, it should be 2.5 twist.

    The answer is B(.5, 1.5, 2.5) but i don't understand why it's given as .5, 1.5 and 2.5 and not just 2.5 twist.
    The reason is that the twists don't all have to be in the same direction. They can be +.5 or .5.
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  5. #5
    Junior Member mathbuoy's Avatar
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    But why can't the other answers apply?
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  6. #6
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    Quote Originally Posted by mathbuoy View Post
    But why can't the other answers apply?
    Because they all include some whole numbers. For an even number of rings, the bottom ring will always have a .5 in its number of twists.
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