1+99=100,2+98=100...49+51=100,一共有50个100,再加上50,等于5050 1+2+3+4+5+6+7+8+9+...98+99+100 =100+(1+99)+(2+98).(49+51)+50 =100×50+50 =5050 或:1+2+3+4+5+6+7+8+9+...98+99+100 =(1+100)x100/2 =5050...