49/140 = (7*7) / (7*20) = 7/20

7/20 = (5*7) / (5*20) = 35/100

15/54 = (3*5) / (3*18) = 5/18

25/40 = (5*5) / (5*8) = 5/8

(25*25) / (25*40) = 625 / 1000

72/320 = (8*9) / (8 * 40) = 9/40

9/40 = (9*25) / (40*25) = 225/1000