2 3/7 = (2*7 + 3) / 7 = (14 + 3) / 7 = 17/7,

5 7/10 = (5*10 + 7) / 10 = (50 + 7) / 10 = 57/10,

13 2/5 = (13*5 + 2) / 5 = (65 + 2) / 5 = 67/5