脱式计算（能简便的要用简便方法计算）

0.8÷0.4×0.15                    1.96÷0.8÷5                12.5×3.4×0.05×0.8

2.07+0.93÷0.3-1.83          8.6×9.9                       0.25×[（23.5+8.5）÷0.8]