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Cloud moderators

11/12/2017 at 15:35
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Two positive integers have a sum of 11 and a product of 24. What is the absolute difference between those two numbers?




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  • ...
    Nguyễn Hưng Phát 11/12/2017 at 17:38

    We have:\(\left\{{}\begin{matrix}a+b=11\\a.b=24\end{matrix}\right.\)\(\Rightarrow ab+a+b=35\Rightarrow ab+a+b+1=36\Rightarrow\left(a+1\right)\left(b+1\right)=36\)

    We have table:(because a,b same kind so not consider a,b negative)

    a+1 1 2 3 4 6 9 12 18 36
    b+1 36 18 12 9 6 4 3 2 1
    a 0 1 2 3 5 8 11 17 35
    b 35(unsatisfactory) 17(unsatisfactory) 1(unsatisfactory) 2(unsatisfactory) 5(unsatisfactory) 3(satisfy) 2(unsatisfactory) 1(unsatisfactory) 0(unsatisfactory)

    So the absolute difference between those two number is:\(\left|8-3\right|=\left|5\right|=5\)

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  • ...
    KEITA FC 8C 19/12/2017 at 12:49

    We have:{a+b=11a.b=24{a+b=11a.b=24⇒ab+a+b=35⇒ab+a+b+1=36⇒(a+1)(b+1)=36⇒ab+a+b=35⇒ab+a+b+1=36⇒(a+1)(b+1)=36

    We have table:(because a,b same kind so not consider a,b negative)

    a+1 1 2 3 4 6 9 12 18 36
    b+1 36 18 12 9 6 4 3 2 1
    a 0 1 2 3 5 8 11 17 35
    b 35(unsatisfactory) 17(unsatisfactory) 1(unsatisfactory) 2(unsatisfactory) 5(unsatisfactory) 3(satisfy) 2(unsatisfactory) 1(unsatisfactory) 0(unsatisfactory)

    So the absolute difference between those two number is:|8−3|=|5|=5

  • ...
    Dao Trong Luan Coordinator 11/12/2017 at 17:26

    So the answer is:

    |15-2| = |2-15| = 13

    ||8-3| = |3-8| = 5

    So the answer is 13 or 5

  • ...
    Dao Trong Luan Coordinator 11/12/2017 at 17:25

    Tell those numbers are a,b

    => a+b = 11 and ab = 24

    => ab - a - b = 24-11 = 13

    => a(b-1) - b + 1 = 14

    => a(b-1) - (b-1) = 14

    => (a-1)(b-1) = 14

    We have table:

    a-1 1 14 2 7
    b-1 14 1 7 2
    a 2 15 3 8
    b 15 2 8 3

    So (a,b) = (2,15); (15,2); (3,8); (8,3)


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