3 17/20÷(3 2/5+1 11/15)= 3 17/20 : (3 6/15 + 1 11/15) = 3 17/20 : 4 17/15 = 77/20 * 15/77 = 3/4;
(1 7/10+4/5)÷1 7/8 = (1 7/10 + 8/10) : 1 7/8 = 1 15/10 : 1 7/8 = 25/8 * 8/15 = 5/3 = 1 2/3;
1 9/35÷(1 1/5+2/3) = 1 9/35 : (1 3/15 + 10/15) = 1 9/35 : 1 13/15 = 44/35 * 15/28 = 33/49;
(8 7/12-2 5/8)÷2 1/6 = (8 14/24 - 2 15/24) : 2 1/6 = 5 23/24 : 2 1/6 = 143/24 * 6/13 = 11/4 = 2 3/4;