12:3 3/8-1 1/4:15/32=

Выполним сначала деление, а после этого отнимание:

12 : 3 3/8 - 1 1/4 : 15/32 = 8/9.

1) 12 : 3 3/8 = 12 : (3 * 8 + 3) / 8 = 12 : (24 + 3) / 8 = 12 : 27/8 = 12 * 8/27 = (12 * 8) / 27 = (4 * 3 * 8) / (3 * 9) = (4 * 8) / 9 = 32/9 = 3 (32 - 3 * 9) / 9 = 3 (32 - 27) / 9 = 3 5/9;

2) 1 1/4 : 15/32 = (1 * 4 + 1) / 4 : 15/32 = 5/4 * 32/15 = (5 * 32) / (4 * 15) = (5 * 4 * 8) / (4 * 5 * 3) = 8/3 = 2 2/3;

3) 3 5/9 - 2 2/3 = 3 - 2 + 5/9 - 2/3 = 1 + 5/9 - (2 * 3) / (3 * 3) = 1 + 5/9 - 6/9 = 1 + (5 - 6) / 9 = 1 - 1/9 = 9/9 - 1/9 = (9 - 1) / 9 = 8/9.