这些怎么巧算 0.64×9.9 0.99×1.001 1.02×4.75

0.64×9.9 =0.64×（10-0.1）=0.64×10-0.64×0.1=6.4-0.064=6.3360.99×1.001 =0.99×(1+0.001)=0.99×1+0.99×0.001=0.99+0.00099=0.990991.02×4.75=(1+0.02)×4.75=4.75+0.02×4.75=4.75+0.095=4.845