脱式计算，能简便的要用简便方法计算．
0.389×4×0.25             4.02×3.02+4.02×6.98
4.05÷0.81+2.4             65.4÷2.5÷4
86×9.9                    1.76﹣[（0.74+0.26）÷0.8]．