3/4 - 1/8 1/5 + 1/6 4/15+2/5 7/10 - 1/2 1/3 - 1/4

Первый пример.

3/4 - 1/8 = 3 * 8/4 * 8 - 1 * 4/8 * 4 = 21/32 - 4/32 = 24 - 4/32 = 20/32 = 5 * 4/8 * 4 = 5/8.

Второй пример. 

1/5 + 1/6 = 1 * 6/5 * 6 + 1 * 5/6 * 5 = 6/30 + 5/30 = 6 + 5/30 = 11/30.

Третий пример.

4/15 + 2/5 = 4 * 5/15 * 5 + 2 * 15/5 * 15 = 20/75 + 30/75 = 20 + 30/75 = 50/75 = 2 * 25/3 * 25 = 2/3.

Четвертый пример.

7/10 - 1/2 = 7 * 2/10 * 2 - 1 * 10/2 * 10 = 14/20 - 10/20 = 14 - 10/20 = 4/20 = 1 * 4/5 * 4 = 1/5.

Пятый пример.

1/3 - 1/4 = 1 * 4/3 * 4 - 1 * 3/4 * 3 = 4/12 - 3/12 = 4 - 3/12 = 1/12