1) вычислите сумму 11/30+7/12, 1/27+5/18, 1/6+1/10+1/15, 3/7+1/6+5/14, 5/12+2/9+1/18, 1/27+5/18, 3/7+1/6+5/14, 1/2+1/3+1/9 2) найдите значение выражения 7

Вычислим сумму дробей:

11/30 + 7/12 = (11 * 2 + 7 * 5) / 60 = (22 + 35) / 60 = 77/60; 1/27 + 5/18 = (1 * 2 + 5 * 3) / 54 = (2 + 15) / 54 = 17/54; 1/6 + 1/10 + 1/15 = (1 * 5 + 1 * 3 + 1 * 2) / 30 = (5 + 3 + 2) / 30 = 10/30 = 1/3; 3/7 + 1/6 + 5/14 = (3 * 6 + 1 * 7 + 5 * 3) / 42 = (18 + 7 + 15) / 42 = (30 + 10) / 42 = 40/42 = 20/21; 5/12 + 2/9 + 1/18 = 5/12 + (2 * 2 + 1 * 1) / 18 = 5/12 + 5/18 = (5 * 3 + 5 * 2) / 36 = (15 + 10) / 36 = 25/36; 1/27 + 5/18 = 17/54; 3/7 + 1/6 + 5/14 = 20/21; 1/2 + 1/3 + 1/9 = (1 * 9 + 1 * 6 + 1 * 2) / 18 = (9 + 6 + 2) / 18 = 17/18.