(7 целых 4/19- 2 целых 8/ 19)+(8целых-4целых 12/19)=

Выполним деянья сначала в скобках, а позже за скобками:

(7 4/19 - 2 8/19) + (8 - 4 12/19) = 8 3/19;

1) 7 4/19 - 2 8/19 = 7 - 2 + 4/19 - 8/19 = 5 + (4 - 8)/19 = 5 - 4/19 = 4 + 1 - 4/19 = 4 + 19/19 - 4/19 = 4 + (19 - 4)/19 = 4 + 15/19 = 4 15/19;

2) 8 - 4 12/19 = 8 - 4 - 12/19 = 4 - 12/19 = 3 + 1 - 12/19 = 3 + 19/19 - 12/19 = 3 + (19 - 12)/19 = 3 + 7/19 = 3 7/19;

3) 4 15/19 + 3 7/19 = 4 + 3 + 15/19 + 7/19 = 7 + (15 + 7)/19 = 7 + 22/19 = 7 + 1 (22 - 19)/19 = 7 + 1 3/19 = 7 + 1 + 3/19 = 8 + 3/19 = 8 3/19.