0.8 * 0.5 = 0.4竖式见图:

0.8*1.7*0.5=0.8*0.5*1.7=0.4*1.7=0.68

0.8x31x1.25简算0.8x31x1.25=0.8x1.25x31=1x31=31

3.8-0.8*1.5-0.5=3.8-(0.8*1.5+0.5)=3.8-(0.8*3*0.5+0.5)=3.8-0.5*(2.4+1)=0.4+3.4-0.5*3.4=0.4+3.4*(1-0.5)=0.4+3.4*0.5=0.4+1.7=2.1

直接计算即可:=70.8-0.4=70.4

化作分数更简便运

0.8*0,5*0,34 =0,4*0.34 =0.136

=3*0.6-0.8*0.6 =(3-0.8)*0.6 =1.32

0.2+0.8x0.5用简便脱式计算方法:=0.2+0.4=0.6

0.8x31x1.25=0.8x1.25x31=1x31=31