An Insane Equation!!

Algebra Level 4

Four positive integers a , b , c , d a, b, c, d are such that

a b c d + a b c + b c d + c d a + d a b + a b + b c + c d + d a + a c + b d + a + b + c + d = 2009. abcd+abc+bcd+cda+dab\\+ab+bc+cd+da+ac+bd+a+b+c+d = 2009 .

What is the value of a + b + c + d a+b+c+d ??

This problem is part of the set Hard Equations


The answer is 73.

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1 solution

Julian Uy
Dec 8, 2014

abcd+abc+bcd+cda+dab+ab+bc+cd+da+ac+bd+a+b+c+d=2009

(a+1)(b+1)(c+1)(d+1)-1=2009

(a+1)(b+1)(c+1)(d+1)=2010

Expressing 2010 as a product of primes, 2010=2x3x5x67.

Therefore, a+b+c+d=(2-1)+(3-1)+(5-1)+(67-1)

=73

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