С, 6 класс: 11/20 - 5/12 = 8/9 + 7/54 = 5/6 - 17/21 = 3/16 + 1/24 = 5/6 - 22/27 = 7/25 - 4/15 = 3/10 + 1/6 = 2/5 - 11/30 = 3/8 + 7/20 = 1/6 - 1/7 = 5/9 + 7/15 = 3/8 + 19/56 = 19/45 - 7/18 = 1/4 - 1/8 = 11/4 + 8/21 =

11/20 - 5/12 =33/60-25/60=8/60=2/15
8/9 + 7/54 =48/54+7/54=55/54=1 1/54
5/6 - 17/21 =35/42-34/42=1/42
3/16 + 1/24 =9/48+2/48=11/48
5/6 - 22/27 =45/54-44/54=1/54
7/25 - 4/15 =21/75-20/75=1/75
3/10 + 1/6 =9/30+5/30=14/30=7/15
2/5 - 11/30 =12/30-11/30=1/30
3/8 + 7/20 =15/40+14/40=29/40
1/6 - 1/7 =7/42-6/42=1/42
5/9 + 7/15 =25/45+21/45=46/45=1 1/45
3/8 + 19/56 =21/56+19/56=40/56=5/7
19/45 - 7/18 =38/90-35/90=3/90=1/30
1/4 - 1/8 =2/8-1/8=1/8
11/4 + 8/21 =231/84+32/84=263/84=
3 11/84

1)11/20-5/12=0,55-5/12=11/20-5/12=2/15
2)8/9+7/54=8+9+7/54=55/54
3)5/6-17/12=5-6-17/2=-7/12
4)3/16+1/24=0,1875+1/24=3/16+1/24=11/48
5)5/6-22/27=5/6-22/27=1/54
6)7/25-4/15=0,28-4/15=7/25-4/14=1/75
7)3/10+1/6=0,3+1/6=3/10+1/6=7/15
8)2/5-11/30=0,4-11/30=2/5-11/30=1/30
9)3/8+7/20=0,375+0,35=29/40
10)1/6-1/7=1/6-7/1=1/42
11)5/9+7/15=5/9+7/15=46/45
12)3/8+19/56=0,375+19/56=3/8+19/56=5/7
13)19/45-7/18=19/45-7/18=1/30
14)1/4-1/8=0,25-0,125=1/8
15)11/4+8/21=2,75+8/21=11/4+8/21=263/84