1) 3/5 + (1/2 - 0,1)

2) 3/14 + 5/21

3) 7/8 - 0,4

4) 2/3 - (4/7 - 1/6)

5) 7/18 + 1/27

6) 0,9 - 5/16

7) 5/6 - (1/2 - 2/7)

1) 3/5 + (1/2-0,1) = 3/5 + (5-1/10) = 3/5 + (4/10) = 3/5+2/5=5/5=1

2) 3/14+5/21=9+10/42=19/42

3) 7/8-4/10=38/80=19/40

4) 2/3 - (4/7-1/6) = 2/3 - (24-7/42) = 2/3-17/42=28-17/42=11/42

5) 7/180+1/27=21+2/54=23/54

6) 9/10-5/16=72/80-25/80=47/80

7) 5/6 - (1/2-2/7) = 5/6 - (7-4/14) = 5/6-3/14=35-9/42=26/42=13/21