3/5 : 1/3 = 3/5 · 3/1 = 9/5 = 1 целая 4/5
2/5 : 7/10 = 2/5 · 10/7 = (2·2)/(1·7) = 4/7
5/9 · 9/10 = 5/10 = 1/2 - сократили на 5
