Vietnam is beautiful

Let set B = { V , I , E , T , N , A , M } B =\left\{ V,I,E,T,N,A,M \right\} with V , I , E , T , N , A , M V,I,E,T,N,A,M are 7 positive whole numbers.

If V + I + E + T + N + A + M = 2016 V+I+E+T+N+A+M=2016 and the set R = { V + I 2 , I + E 2 , E + T 2 , T + N 2 , N + A 2 , A + M 2 , M + V 2 } R =\left\{ \frac { V+I }{ 2 } ,\frac { I+E }{ 2 } ,\frac { E+T }{ 2 } ,\frac { T+N }{ 2 } ,\frac { N+A }{ 2 } ,\frac { A+M }{ 2 } ,\frac { M+V }{ 2 } \right\} is a permutation of set B B , what is the value of M M ?


The answer is 288.

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1 solution

Linkin Duck
Apr 3, 2017

By applying AM-GM inequality we have

( V + I 2 ) 2 V 2 + I 2 2 , ( I + E 2 ) 2 I 2 + E 2 2 , ( E + T 2 ) 2 E 2 + T 2 2 , . . . ( M + V 2 ) 2 M 2 + V 2 2 . ( V + I 2 ) 2 + ( I + E 2 ) 2 + . . . + ( M + V 2 ) 2 V 2 + I 2 + E 2 + . . . + M 2 ( 1 ) { \left( \frac { V+I }{ 2 } \right) }^{ 2 }\le \frac { { V }^{ 2 }+{ I }^{ 2 } }{ 2 } ,\\ { \left( \frac { I+E }{ 2 } \right) }^{ 2 }\le \frac { { I }^{ 2 }+{ E }^{ 2 } }{ 2 } ,\\ { \left( \frac { E+T }{ 2 } \right) }^{ 2 }\le \frac { { E }^{ 2 }+{ T }^{ 2 } }{ 2 } ,\\ ...\\ { \left( \frac { M+V }{ 2 } \right) }^{ 2 }\le \frac { { M }^{ 2 }+{ V }^{ 2 } }{ 2 } .\\ \Longrightarrow { \left( \frac { V+I }{ 2 } \right) }^{ 2 }+{ \left( \frac { I+E }{ 2 } \right) }^{ 2 }+...+{ \left( \frac { M+V }{ 2 } \right) }^{ 2 }\le { V }^{ 2 }+{ I }^{ 2 }+{ E }^{ 2 }+...+{ M }^{ 2 } \quad \left( 1 \right)

Furthermore, R R is a permutation of B B { ( V + I 2 ) 2 , ( I + E 2 ) 2 , ( E + T 2 ) 2 . . . , ( M + V 2 ) 2 } \Longrightarrow \left\{ { \left( \frac { V+I }{ 2 } \right) }^{ 2 },{ \left( \frac { I+E }{ 2 } \right) }^{ 2 },{ \left( \frac { E+T }{ 2 } \right) }^{ 2 }...,{ \left( \frac { M+V }{ 2 } \right) }^{ 2 } \right\} is a permutation of { V 2 , I 2 , E 2 , . . . , M 2 } \left\{ { V }^{ 2 },{ I }^{ 2 },{ E }^{ 2 },...,{ M }^{ 2 } \right\}

which leads to ( V + I 2 ) 2 + ( I + E 2 ) 2 + ( E + T 2 ) 2 + . . . + ( M + V 2 ) 2 = V 2 + I 2 + E 2 + . . . + M 2 ( 2 ) { \left( \frac { V+I }{ 2 } \right) }^{ 2 }+{ \left( \frac { I+E }{ 2 } \right) }^{ 2 }+{ \left( \frac { E+T }{ 2 } \right) }^{ 2 }+...+{ \left( \frac { M+V }{ 2 } \right) }^{ 2 }={ { V }^{ 2 }+{ I }^{ 2 }+{ E }^{ 2 }+...+{ M }^{ 2 } }\quad \left( 2 \right)

From ( 1 ) , ( 2 ) \left( 1 \right) ,\left( 2 \right) V = I = E = T = N = A = M = 2016 7 = 288 . \Longrightarrow V=I=E=T=N=A=M=\frac { 2016 }{ 7 } =\boxed { 288 } .

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