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Math Help - find the remainder

  1. #1
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    find the remainder

    find the remainder when-



    is divided by 10.

    No idea.

    i just know the sum of n.n!=(n+1)!-1
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  2. #2
    Behold, the power of SARDINES!
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    Quote Originally Posted by adhyeta View Post
    find the remainder when-



    is divided by 10.

    No idea.

    i just know the sum of n.n!=(n+1)!-1
    Notice for n \ge 5 each term is divisable by 10 so they have a remainder of zero(why)

    Now we only need to worry about the first 4 terms

    We also don't need to worry about the 4 term (why)

    so we get (2)1+(6)2+12(6)=86 so the remainder is 6
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  3. #3
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    Quote Originally Posted by TheEmptySet View Post
    Notice for n \ge 5 each term is divisable by 10 so they have a remainder of zero(why)

    Now we only need to worry about the first 4 terms

    We also don't need to worry about the 4 term (why)

    so we get (2)1+(6)2+12(6)=86 so the remainder is 6
    yes for the fourth term too we have 16+4=20 (hence, divisible by 10)

    thank you.
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