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Math Help - very quick modulo question

  1. #1
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    very quick modulo question

    What is 10 x -38 mod 11?

    What is 16 x -80 mod 16?

    What is 278-421 mod 19?
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  2. #2
    MHF Contributor Bruno J.'s Avatar
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    10\times -38 \equiv -1 \times -38 \equiv 5 \mod 11

    16\times -80 \equiv 0 \times -80 \equiv 0 \mod 16

    278\times -421 \equiv 12 \times -3 \equiv 17 \mod 19
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    Shouldnt i get numerical answers?

    I got 9 for the 3rd one....
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  4. #4
    Super Member Bacterius's Avatar
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    No it is indeed 17 for the last one, because 278 \equiv 12 \ \ \ \  [19] and -421 \equiv -3 \ \ \ \  [19].

    EDIT : ah yes chiph588@ you are right, but why put a substraction question following two multiplication questions ? This is confusing
    Last edited by Bacterius; December 3rd 2009 at 03:56 PM.
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  5. #5
    MHF Contributor chiph588@'s Avatar
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    For the third are you wanting  278\cdot(-421) \mod{19} or  (278-421) \mod{19} ?

    If it is the latter, then  9 is the correct answer.
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