用竖式计算.
口算:12×30= 75÷25= 420÷70= 21×700= 11×40=124÷4= 104×20= 589﹣90= 2×7×5= 50×12=
÷50=0.12=.
= :24=5:8= :40= %
3÷ ==0.75=6: = %
3÷ ==0.6=6: = %.