用简便方法计算1+2-3+4-5+...+98-99+100

1+2-3+4-5+...+98-99+100={1+[(100+2)-(99+3)+(98+4)-(97+5)+...+(4+98)-(3+99)]+(2+100)+1}/2=[1+(102-102+102-102+...+102-102)+102+1]/2=(1+102+1)/2=104/2=52