А)18/19-7/19+3/19: б)2/7+4/7-5/7: в)9/11-3/11-2/11: г)5/12+3/12+3/12 д)11/15-(3/15+7/15) е)13/16-(13/16-3/16).

Вычислим значения выражений:

1) 18/19 - 7/19 + 3/19 = (18 - 7 + 3)/19 = (11 + 3)/19 = 14/19;

2) 2/7 + 4/7 - 5/7 = (2 + 4 - 5)/7 = (6 - 5)/7 = 1/7;

3) 9/11 - 3/11 - 2/11 = (9 - 3 - 2)/11 = (6 - 2)/11 = 4/11;

4) 5/12 + 3/12 + 3/12 = (5 + 3 + 3)/12 = (8 + 3)/12 = 11/12;

5) 11/15 - (3/15 + 7/15) = 11/15 - (3 + 7)/15 = 11/15 - 10/15 = (11 - 10)/15 = 1/15;

6) 13/16 - (13/16 - 3/16) = 13/16 - (13 - 3)/16 = 13/16 - 10/16 = (13 - 10)/16 = 3/16.