Ответ:

Пошаговое объяснение:

1) 4/5 + 3/7 = 28/35 + 15/35 = 43/35

2) 5/12 + 9/20 = 25/60 + 27/60 = 52/60 = 13/15

3) 5/18 + 4/45 = 25/90 + 8/90 = 33/90 = 11/30

4) 12/17 + 27/34 = 24/34 + 27/34 = 51/34 = 3/2 = 2. 1/2

5) 5/9 - 7/18 = 10/18 - 7/18 = 3/18 = 1/6

6) 11/12 - 1/4 = 11/12 - 3/12 = 8/12 = 2/3

7) 8/21 - 4/35 = 40/105 - 12/105 = 28/105 = 4/15

8) 11/63 - 5/42 = 22/126 - 10/126 = 12/126 = 2/21