Ответ:

2/5; 23 3/4; 1/3; 1

Пошаговое объяснение:

1) 2 4/5 : 7 = 14/5 : 7/1  = 14/5 х 1/7 = 2/5

2) 19 : 4/5 = 19/1 х 5/4 = 95/4 = 23 3/4

3) 5 1/6 : 15 1/2 = 31/6 : 31/2 = 31/6 х 2/31 = 1/6 х 2/1 = 1/3

4) (1/2 + 1/3) : 5/6 = (3/6 + 2/6) : 5/6 = 5/6 : 5/6 = 1