1) (6/21 + 5/21) * 7/11 = 11/21 * 7/11 = 1/3
2) (16/22 + 3/22) * 11/5 = 19/22 * 11/5 = 38/5
3) 19/12 : (9/24 +10/24) = 19/12 : 19/24 = 19/12 * 24/19 = 2
4) 17/36 : (21/36 - 20/36) = 17/36 * 36/1 = 17
5) (3/14 + 10/14) * 7/26 = 13/14 * 7/26 = 1/4
6) 19/24 : (9/24 + 10/24) = 1