8 целых 8/15-4 целых 9/20= 7 целых 1/10-3целых 1/6=

Первый пример.

8 8/15 - 4 9/20 = 4 1/12

8 8/15 - 4 9/20 = 8 * 15 + 8/15 - 4 * 20 + 9/20 = 128/15 - 89/20 = 128 * 20/15 * 20 - 89 * 15/20 * 15 = 2560/300 - 1335/300 = 2560 - 1335/300 = 1225/300 = 49 * 25/12 * 25 = 49/12 = 1 + 4 * 12/12 = 4 1/12.

Второй пример.

7 1/10 - 3 1/6 = 3 14/15;

7 1/10 - 3 1/6 = 7 * 10 + 1/10 - 3 * 6 + 1/6 = 71/10 - 19/6 = 71 * 6/10 * 6 - 19 * 10/6 * 10 = 426/60 - 190/60 = 426 - 190/60 = 236/60 = 59 * 4/15 * 4 = 59/15 = 14 + 3 * 15/15 = 3 14/15.