Вычислите: 1) 12: 3,2+(6-(3 7/8-1 5/6)*6/7); 2) (4 6/7: (5/6+8/21)-2 5/13)*8 2/3.

1) 12:3,2+(6-(3 7/8-1 5/6)*6/7) = 8,

1) 12 : 3,2 = 3,75,
2) 3 7/8 - 1 5/6 = 31/8 - 11/6 = 93/24 - 44/24 = 49/24 = 2 1/24,
3) 2 1/24 * 6/7 = 49/24 * 6/7 = 7/4 = 1 3/4  (или 1,75),
4) 6 - 1,75 = 4,25,
5) 3,75 + 4,25 = 8,

2) (4 6/7:(5/6+8/21)-2 5/13)*8 2/3 = 14,

1) 5/6 + 8/21 = 35/42 + 16/42 = 51/42 = 17/14 = 1 3/14,
2) 4 6/7 : 1 3/14 = 34/7 : 17/14 = 34/7 * 14/17 = 2 * 2 = 4,
3) 4 - 2 5/13 = 1 8/13,
4) 1 8/13 * 8 2/3 = 21/13 * 26/3 = 2 * 7 = 14