12：4/3
=12×3/4:4/3×3/4
=9:1
2/9:4/3
=2/9×9/2:4/3×9/2
=1:6
3.2:0.8
=4:1
42:7
=6:1
25/125
=1:5
2.48:80
=2.48÷8:80÷8
=0.31:10
=31:1000