（1）2 .58 ×1 .9

        =2.58×(2-0.1)

        =2.58×2-2.58×0.1

        =5.16-0.258

        =4.902（2）10 .8 ÷1 .2

        =10.8÷(0.2×6)

        =10.8÷0.2÷6

        =54÷6

        =9

（3）4 .5 ÷0 .5 ÷9

        =4.5÷(0.5×9)

        =4.5÷4.5

        =1（4）0 .32 ×1 .25 ×0 .25

       =(0.4×0.8)×1.25×0.25

       =(0.8×1.25)×(0.4×0.25)

       =1×0.1

       =0.1