(6 4/5 - 2 3/4) : (2 16/21 + 3 2/3) 1) 6 4/5 - 2 3/4 = 6 (4 * 4)/20 - 2 (5 * 3)/20 = 6 16/20 - 2 15/20 = (6 - 2) + (16 - 1)/20 = 4 1/20. 2) 2 16/21 + 3 2/3 = 2 16/21 + 3 14/21 = 5 30/21 = 6 9/21. 3) 4 1/20 : 6 9/21 = 81/20 : 135/21 = 81/20 * 21/135 = 9/20 * 21/15 = 3/20 * 21/5 = 63/100.