# [10,20] is a Problem!

Algebra Level 4

$\displaystyle S_n = \sum _{ r=1 }^{ n }{ \big[(r-10)(r-20) \big] }$

Given the above function of $$S_n$$, what does the summation below equal to?

$\displaystyle \sum _{ r=1 }^{ 50 } \big|(r-10)(r-20)\big|$

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