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Math Help - 3digit numbers that are multiples of 7 with individual digits that add to 7.

  1. #1
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    3digit numbers that are multiples of 7 with individual digits that add to 7.

    how can i find all the 3 digit numbers that are multiples of seven with individual digits that add to 7? I've been trying to figure this out using modular arithmetic, but I think I'm doing it wrong.
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  2. #2
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    Quote Originally Posted by qtpipi View Post
    how can i find all the 3 digit numbers that are multiples of seven with individual digits that add to 7?
    Using the floor function \left\lfloor {\dfrac{{999}}{7}} \right\rfloor  - \left\lfloor {\dfrac{{99}}{7}} \right\rfloor .

    Tell us why that works.
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  3. #3
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    the floor function just gives us the number of 3 digit numbers that are multiples of 7. i need to find which of these multiples of 7 have individual digits that add to 7.
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    Quote Originally Posted by qtpipi View Post
    the floor function just gives us the number of 3 digit numbers that are multiples of 7. i need to find which of these multiples of 7 have individual digits that add to 7.
    Sorry, I read the question too quickly.
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  5. #5
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    figured it out!
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