1+2+3+4+5+6+7+8+9+10+11+12+13+14+15.+99+100
问题描述:
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15.+99+100
答
(首项+末项)x项数/2
=(1+100)x100/2
=101x50
=5050