18分之7:54分之21
=7/18:21/54
=21:21
=1:1
0.25:0.75
=25:75
=1:3
5分之2:4
=2/5:4
=2:20
=1:10
1.5:90
=3:180
=1:60
4：8分之1
=4:1/8
=32:1
5cm:5km
=5cm:500000cm
=1:500000