№ 685
3/5-1/5=2/5
7/20-3/20=4/20=1/5
12/16-3/16=9/16
16/27-8/27=8/27
№ 866
1/2-1/4=2/4-1/4=1/4
5/9-1/3=5/9-3/9=2/9
7/10-3/5=7/10-6/10=1/10
16/27-1/9=16/27-3/27=13/27
3/5-13/45=27/45-13/45=14/45
1/3-8/27=9/27-8/27=1/27
1/2-1/3=3/6-2/6=1/6
3/5-1/3=9/15-5/15=4/15
7/8-2/3=21/24-16/24=5/14
3/4-4/7=21/28-16/28=5/28
9/16-11/24=27/48-22/48=5/48
11/12-11/18=33/36-22/36=11/36