$$2+4 +6 +8=1+3 +5 +7 +$$~\uline{~~~~~~~~~~}~. 
Overseas Competition->Knowledge Point->Calculation Modules->Whole Numbers->Whole Numbers Addition and Subtraction 
$$2+4 +6 +8=1+1+3+1+5+1+7+1=1+3 +5 +7 +4$$. 