6-2/3 - 4/21
5-1/2 - 3-1/5
10-2/3 - 6-1/6
3-1/6 + 1-1/30
3-4/5 - 1-2/15
8 - 3-2/7
11 - 5-2/5

6-2/3 - 4/21=(6*21-2*7-4)/21=108/21=5 3/21

5-1/2 - 3-1/5=2-1/2-1/5=1,5-0,2=1,3=1 3/10

10-2/3 - 6-1/6=4-4/6-1/6=4-5/6=3+6/6-5/6=3 1/6

3-1/6 + 1-1/30=4-1/6-1/30=4-5/30-1/30=4-1/5=3 4/5

3-4/5 - 1-2/15=2-4/5-2/15=2-(12-2)/15=2-2/3=1 1/3

8 - 3-2/7=5-2/7=4 5/7

11 - 5-2/5 =6-2/5=5 3/5