35=5*7
24=2*2*2*3
НОК=35*24=840
1. 15 7/11 - 4 9/16 + 3 4/11 = 15 7/11 + 3 4/11 - 4 9/16 = 18 11/11- 4 9/16 = 19 - 4 9/16 = 18 16/16 - 4 9/16 = 14 7/16
2. 12 4/13 - 2 13/20 + 3 9/13 = 12 4/13 + 3 9/13- 2 13/20 = 15 13/13 - 2 13/20 = 16 - 2 13/20 = 15 20/20 - 2 13/20 = 13 7/20
2 3/4 - 1 5/6= 2 9/12 - 1 10/12 =11/12
Ответ:11/12