（5/9）/（x/4）=y/27
20/9x=y/27
xy=60
1 * 60 =60
2 * 30 =60
3 * 20 =60
4 * 15 =60
5 * 12 =60
6 * 10 =60
10 * 6 =60
12 * 5 =60
15 * 4 =60
20 * 3 =60