We say that a quadruple $(A,B,C,D)$ is dobarulho when $A,B,C$ are non-zero algorisms and $D$ is a positive integer such that: $1.$ $A \leq 8$ $2.$ $D>1$ $3.$ $D$ divides the six numbers $\overline{ABC}$, $\overline{BCA}$, $\overline{CAB}$, $\overline{(A+1)CB}$, $\overline{CB(A+1)}$, $\overline{B(A+1)C}$. Find all such quadruples.
Problem
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Tags: Brazil
NikoIsLife
17.11.2018 03:54
We find that
$$D|\overline{ABC}+\overline{BCA}+\overline{CAB}=111(A+B+C)$$and
$$D|\overline{(A+1)CB}+\overline{CB(A+1)}+\overline{B(A+1)C}=111(A+B+C)+111$$So, $D$ must be a divisor of $111$. This gives $3$ possible cases.
Case I. $D=3$
Note that $\overline{ABC}\equiv A+B+C\pmod3$ and $\overline{(A+1)CB}\equiv A+B+C+1\pmod3$ which means that they cannot both be divisible by $3$ at the same time. Therefore, $D$ cannot be divisible by $3$.
Case II. $D=37$
Then, $\overline{(A+1)CB}-\overline{ABC}=100-9B+9C\equiv\pmod{37}\implies B-C\equiv7\pmod{37}$. This gives $(B,C)=(7,0),(8,1),(9,2)$.
If $(B,C)=(7,0)$, then $37|\overline{A70}\implies A\equiv3\pmod{37}$
If $(B,C)=(8,1)$, then $37|\overline{A81}\implies A\equiv4\pmod{37}$
If $(B,C)=(9,2)$, then $37|\overline{A92}\implies A\equiv5\pmod{37}$
This gives $(3,7,0,37),(4,8,1,37),(5,9,2,37)$.
Case III. $D=111$
Similar to Case I.
Thus, the only solutions are $(A,B,C,D)=\boxed{(3,7,0,37),(4,8,1,37),(5,9,2,37)}$.
Ilove_mathematics
17.11.2018 17:32
NikolsLife on the question is said that $A, B, C$, are non-zero algarisms! So $(3,7,0,37)$ isn't solution. Thus the solutions are: $(A, B, C, D) = (4, 8, 1, 37)$ and $(5, 9, 2, 37)$.