$$11+ 12 + 13 + 14 + 15 = 1 + 2 + 3 + 4 + 5 +$$． 
Overseas Competition->Knowledge Point->Calculation Modules->Whole Numbers->Whole Numbers Addition and Subtraction 
$$1+10 + 2+10 + 3+10 + 4+10 + 5+10 = 1+2+3+4+5 + 50$$. 