(1+0.1)+(2+0.1x2)+(3+0.1x3)+...+(99+0.1x99)+(100+0.1x99)
=(1+2+3+……+99+100)+(0.1+0.1×2+0.1×3+……+0.1×99+0.1×100)
=(1+2+3+……+99+100)+(0.1+0.2+0.3+……+9.9+×10.)
=(1+100)×100÷2+(0.1+10)×100÷2
=5050+505
=5555
(1+0.1)+(2+0.1x2)+(3+0.1x3)+...+(99+0.1x99)+(100+0.1x99)
=(1+2+3+……+99+100)+(0.1+0.1×2+0.1×3+……+0.1×99+0.1×100)
=(1+2+3+……+99+100)+(0.1+0.2+0.3+……+9.9+×10.)
=(1+100)×100÷2+(0.1+10)×100÷2
=5050+505
=5555