С начала сократи дроби, затем сложить
3/12+50/60
15/36+28/54
25/45+2/60
21/30+6/45​

Пошаговое объяснение:

1) 3/12 = 1/4

50/60 = 5/6

1/4 + 5/6 = 6/24 + 20/24 = 26/24 = 13/12 = 1 целая 1/12

2) 15/36 = 5/12

28/54 = 14/27

5/12 + 14/27 = 45/108 + 56/108 = 101/108

3) 25/45 = 5/9

2/60 = 1/30

5/9 + 1/30 = 50/90 + 3/90 = 53/90

4) 21/30 = 7/10

6/45 = 2/15

7/10 + 2/15 = 21/30 + 4/30 = 25/30 = 5/6