1.1+1.3+1.5+1.7+1.9+1.11+1.13+1.15+1.17+1.19+1.21+......+1.99

162.85

1.1+1.3+1.5+1.7+1.9 先算,
对于相差一样的,有一个公式
首项加末项,乘于 项数除于2,就是和了.

所以

(1.1+1.9)*5/2=7.5
(1.11+1.99)*45/2 =69.75

和是77.25

1.1+1.3+1.5+1.7+1.9+1.11+1.13+1.15+1.17+1.19+1.21+......+1.99
=(1.1+1.3+1.5+1.7+1.9)+(1.11+1.13+1.15+1.17+1.19+1.21+......+1.99)=7.5+45*(1.11+1.99)/2=77.25