其它
Calculate: $$1+2+3+\ldots\ldots+37+38+39+40+39+38+37+\ldots\ldots+13+12+11$$=~\uline{~~~~~~~~~~}~ 
Overseas Competition->Knowledge Point->Calculation Modules->Whole Numbers->Whole Numbers Addition and Subtraction 
$$1+2+3+\ldots\ldots+37+38+39+40+39+38+37+\ldots\ldots+13+12+11$$  $$=（1+2+3+\ldots\ldots+37+38+39+40+39+38+37+\ldots\ldots+3+2+1）-（1+2+3+\ldots\ldots+8+9+10）$$  $$=40\times40-55$$  $$=1545.$$ 