2.2*0.4*1.25*2.6=1.1*0.8*1.25*2.6=1.1*2.6=2.86
1.625+2.625+3.625+…+80.625 =1+2+……+80+0.625*80
5.5*6.6+6.6*7.7+7.7*8.8+8.8*9.9=1.21*（5*6+6*7+7*8+8*9）