1 4/7 + 2 3/21 ; 5 1/4 + 3 8/11
4 -2/3 ; 5 1/4- 3 7/8

Пошаговое объяснение:

1 4/7 + 2 3/21  = 1 4/7  + 2 1/7 = 3 5/7;

5 1/4 + 3 8/11  = 5 11/44 + 3 32/44 = 8 43/44

4 -2/3 = 3 3/3 - 2/3 = 3 1/3 ;

5 1/4- 3 7/8 = 5 2/8 - 3 7/8 = 4 10/8 - 3 7/8 = 1 3/8