2. Вычислите: 1) 13/21 - 11/28 * 8/33; 2) 1/3 + 2/5 : 3/35; 3) 7/39 * (1/7 + 6/49);

1. 13/21 - (11*8)/(28*33) = 13/21 - 88/924 = 13/21 - 2/21 = 11/21.
2. 1/3 + (2/5) * (35/3) = 1/3 + 70/15 = 1/3 + 14/3 = 15/3 = 5.
3. 7/39 * (7/49 + 6/49) = 7/39 * (13/49) = (7*13)/(39*49) = 91/1911 = 1/21.