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Lê Quốc Trần Anh Coordinator

01/08/2017 at 09:04
Answers
2
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Find a 4-digit positive number \(abcd\) given:

\(a^a+\left[b,c,d\right]=100\)




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  • ...
    Phan Thanh Tinh Coordinator 01/08/2017 at 18:47

    Condition : \(a,b,c,d\in N;a,b,c,d< 10;a\ne0\)

    \(\left[b,c,d\right]\ge0\Rightarrow a^a\le100\Rightarrow a\in\left\{1;2;3\right\}\)

    If a = 1,then \(\left[b,c,d\right]=100-1^1=99=3^2.11\)

    So,there'll be at least 1 number that have the factor 11 in its/their form of prime factorization (asburd since b,c,d < 10)

    If a = 2,then \(\left[b,c,d\right]=100-2^2=96=2^5.3\)

    So,there'll be at least 1 number that have the factor 25 in its/their form of prime factorization (asburd)

    If a = 3,then \(\left[b,c,d\right]=100-3^3=73\)

    So,there'll be at least 1 number that have the factor 73 in its/their form of prime factorization (asburd)

    Hence,there's no satisfied number

    Lê Quốc Trần Anh selected this answer.
  • ...
    Dao Trong Luan 01/08/2017 at 20:02

    We have a,b,c,d are four digits so \(0\le a,b,c,d\le9\)

    Because aa + [b,c,d] = 100

    => aa \(\le100\)=> a \(\in\left\{1,2,3\right\}\)

    If a = 1

    => [b,c,d] = 100 - 1 = 99 = 9.11

    But 11 has two digits so b,c,d unsatisfactory 

    If a = 2

    => [b,c,d] = 100 - 22 = 96 = 3.32

    But 32 has two digits so b,c,d unsatisfactory 

    If a = 3

    => [b,c,d] = 100 - 33 = 73 

    But 73 has two digits so b,c,d unsatisfactory 

    Therefore, there are no numbers satisfying the question 


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