Ответ:

7. х = 7

8. 4 25/42

Пошаговое объяснение:

7. (3/7х-5/6) * 1 2/13 = 2 1/2

(3/7х-5/6) * 15/13 = 5/2

45/91х - 75/78 = 5/2

45/91х = 5/2 + 75/78

45/91х = 195/78 + 75/78

45/91х = 270/78

х = 270/78 : 45/91 = 270/78 * 91/45

х = 7

8. 7 2/3+(6-2 4/7) : 2 2/5 - 4,5 = 4 25/42

По действиям:

1. 6 - 2 4/7 = 3 3/7

2. 3 3/7 : 2 2/5 = 24/7 * 5/12 = 10/7 = 1 3/7

3. 7 2/3 + 1 3/7 = 7 14/21 + 1 9/21 = 8 23/21 = 9 2/21

4. 9 2/21 - 4,5 = 9 2/21 - 4 1/2 = 9 4/42-4 21/42 = 8 46/42-4 21/42 = 4 25/42