0.6:1.8=7:21
0.6:7=1.8:21
1.8:0.6=21:7
7:0.6=21:1.8
7:21=0.6:1.8
1.8:21=0.6:7
21:7=1.8:0.6
21:1.8=7:0.6
共计8个