1.08－0.8=1.08－1＋0.2=0.28
（0.18＋0.9）÷9
=0.18÷9＋0.9÷9
=0.02＋0.1
=0.12
6.3÷0.01
=（6.3×100）÷（0.01×100）
=630÷1
=630
4.9×9＋4.9
=4.9×（9＋1）
=4.9×10
=492.5*4*0.8*1.25呢？