10.75+0.4+9.86
=10.75+0.4+(10-0.14)
=10.75+0.4+10-0.14
=(10.75+10)+(0.4-0.14)
=20.75+0.26
=21.01我们不学小数拆分凑小数的，只学了结合律和连减打包律