原式=3.35×（100-1）×2+6.7 =（3.35×100-3.35）×2+6.7 =335×2 =670
3.35*99*2+6.7=3.35x2x99+6.7=6.7x99+6.7x1=6.7x(99+1)=6.7x100=670
3.35*(100-1)*2-6.7=335-6.7+6.7=335
（3.35x2）x100
