1+2+3+4+5+6+7...................+998+999+1000
=(1+1000)+(2+999)+(3+998)+...+(500+501)
=(1+1000)*500
=1001*500
=500500
1+2+3+4.......+998+999+1000
=(1+1000)×1000÷2
=1001×500
=500500
解:1+2+3+4.......+998+999+1000
=(1+1000)*1000/2
=500500
1+2+3+4.......+998+999+1000=(1+1000)*500=1001*500=500500
(1+1000)*1000*1/2=500500