$1+3+5+7+9+ 11 + 13+ 15+17 +19=$~\uline{~~~~~~~~~~}~． 
Overseas Competition->Knowledge Point->Calculation Modules->Whole Numbers->Whole Numbers Addition and Subtraction 
$1+3+5+7+9+ 11 + 13+ 15+17 +19=10^{2}=100$ 