А) (1/4 + 2/3 - 1/2) / (1/2 - 1/4 + 2/3) = 5/11
1) 1/4 + 2/3 - 1/2 = 3/12 + 8/12 - 6/12 = 5/12
2) 1/2 - 1/4 + 2/3 = 6/12 - 3/12 + 8/12 = 11/12
3) 5/12 : 11/12 = 5/12 * 12/11 = 5/11
b) (3/5 - 1/3 - 2/9) / (7/15 + 2/3 - 4/5) = 2/15
1) 27/45 - 15/45 - 10/45 = 2/45
2) 7/15 + 2/3 - 4/5 = 7/15 + 10/15 - 12/15 = 5/15 = 1/3
3) 2/45 : 1/3 = 2/45 * 3 = 6/45 = 2/15