4/9:2,5/7:3,10/21:5,9/10:15,3/7:21

4/9 / 2 = 2/9 5/7 / 3 = 5/21 10/21 / 5 = 2/21 9/10 / 15 = 3/50 3/7 / 21 = 1/49