12/52:81/65; 30 - ((8 3/4-6 1/2) : 1/8+11 3/7)

Вычислим выражения:

1) 12/52 : 81/65 = 12/52 * 65/81 = 4/52 * 65/27 = 2/26 * 65/27 = 2/2 * 5/27 = 1 * 5/27 = 5/27;

2) 30 - ((8 ¾ - 6 1/2) / (1/8 + 11 3/7)) = 30 - (2 + ¾ - ½) / (1/8 + 80/7) = 30 - (2 + ¾ - 2/4) / (7/56 + 640/56) = 30 - (2 + ¼) / (647/56) = 30 - (9/4) / (647/56) = 30 - 9/4 * 56/647 = 30 - 9/1 * 14/647 = 30 - 126/647 = 29 + 647/647 - 126/647 = 29 + 521/647 = 29 521/647.