(1/12 - 1/20) : 1/5 - 1/6 = 0,
1) 1/12 - 1/20 = 5/60 - 3/60 = 2/60 = 1/30,
2) 1/30 : 1/5 = 1/30 * 5/1 = 1/6,
3) 1/6 - 1/6 = 0,
20 : 5 1/3 + 4/5 * 5 3/16 = 7 9/10,
1) 20 : 5 1/3 = 20 : 16/3 = 20 * 3/16 = 15/4 = 3 3/4,
2) 4/5 * 5 3/16 = 4/5 * 83/16 = 83/20 = 4 3/20,
3) 3 3/4 + 4 3/20 = 3 15/20 + 4 3/20 = 7 18/20 = 7 9/10,
(4 1/4 * 1/4) : (9 3/8 - 8 5/16) = 1,
1) 4 1/4 * 1/4 = 17/4 * 1/4 = 17/16 = 1 1/16,
2) 9 3/8 - 8 5/16 = 9 6/16 - 8 5/16 = 1 1/16,
3) 1 1/16 : 1 1/16 = 1