1.999*4.9+1.99*5.1=1.99*4.9+0.009*4.9+1.99*5.1
=1.99(4.9+5.1)+0.009*4.9
=19.9+0.0441
=19.9441
19.99乘0.49+1.99乘5.1=多少怎样用简便方法计算
1.999*4.9+1.99*5.1=1.99*4.9+0.009*4.9+1.99*5.1
=1.99(4.9+5.1)+0.009*4.9
=19.9+0.0441
=19.9441