1) 4 1\2÷2 1\4= 2) 2 4\5÷1 2\5= 3) 7\9÷2 1\3 = 4) 8 1\2÷19\20=.

1) 4 1\\2 : 2 1\\4 = (2 * 4 + 1 / 2) : (4 * 2 + 1 / 4) = 9/2 : 9/4 = 9/2 * 4/9 = 4/2 = 2;

2) 2 4\\5 : 1 2\\5 = 14/5 : 7/5 = 14/5 * 5/7 = 14/7 = 2; 

3) 7\\9 : 2 1\\3 = 7/9 : 7/3 = 7/9 * 3/7 = 9/3 = 3;

4) 8 1\\2 : 19\\20 = 17/2 : 19/20 = 17/2 * 20/19 = 17/1 * 10/19 = 170/19 = 8 18/19.