1) 4 33/40-3 19/30 2)8 8/9-5 11/15 3) 8 1/12-2 7/20

Первый пример.

4 33/40 - 3 19/30 = 4 * 40 + 33/40 - 3 * 30 + 19/30 = 193/40 - 109/30 = 193 * 30/40 * 30 - 109 * 40/30 * 40 = 5790/1200 - 4360/1200 = 5790 - 4360/1200 = 1430/1200 = 143 * 10/120 * 10 = 143/120 = 23 + 1 * 120/120 = 1 23/20;

Второй пример. 

8 8/9 - 5 11/15 = 8 * 9 + 8/9 - 5 * 15 + 11/15 = 80/9 - 86/15 = 80 * 15/9 * 15 - 86 * 9/15 * 9 = 1200/135 - 774/135 = 1200 - 774/135 = 426/135 = 142 * 3/45 * 3 = 142/45 = 7 + 3 * 45/45 = 3 7/45;

Третий пример.

8 1/12 - 2 7/20 = 8 * 12 + 1/12 - 2 * 20 + 7/20 = 97/12 - 47/20 = 97 * 20/12 * 20 - 47 * 12/20 * 12 = 1940/240 - 564/240 = 1940 - 564/240 = 1376/240 = 86 * 16/15 * 16 = 86/15 = 11 + 5 * 15/15 = 5 11/15.