2/5 : 1/3 = 2/5 * 3/1 = 6/5 = 6 : 5
5/6 : 3/8 = 5/6 * 8/3 = (5*4)/(3*3) = 20/9 = 20 : 9
1 5/12 : 2/15 = 17/12 * 15/2 = (17*5)/(4*2) = 85/8 = 85 : 8
4/7 : 1/2 = 4/7 * 2/1 = 8/7 = 8 : 7
3 1/9 : 2 1/6 = 28/9 : 13/6 = 28/9 * 6/13 = (28*2)/(3*13) = 56/39 = 56 : 39
1/8 : 1 7/12 = 1/8 : 19/12 = 1/8 * 12/19 = (1*3)/(2*19) = 3/38 = 3 : 38