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 11/14+8/21 11/20-5/12 8/9+7/54 5/6-17/21

1. 7/25 - 4/15 = 21/75 - 20/75 = 1/75;

2. 3/10 + 1/6 = 9/30 + 5/30 = 14/30 = 7/15;

3. 2/5 - 11/30 = 12/30 - 11/30 = 1/30;

4. 3/8 + 7/20 = 15/40 + 14/40 = 19/40; 

5. 1/6 - 1/7 = 7/42 - 6/42 = 1/42;

6. 5/9 + 7/15 = 25/45 + 21/45 = 46/45 = 1 1/45;

7. 3/8 + 19/56 = 21/56 + 19/56 = 40/56 = 5/7;

8. 19/45 - 7/18 = 38/90 - 35/90 = 3/90 = 1/30;

9. 1/4 - 1/8 = 2/8 - 1/8 = 1/8;

10. 11/14 + 8/21 = 33/42 + 16/42 = 49/42 = 1 7/42 = 1 1/6;

11. 11/20 - 5/12 = 33/60 - 25/60 = 8/60 = 2/15;

12. 8/9 + 7/54 = 48/54 + 7/54 = 55/54 = 1 1/54;

13. 5/6 - 17/21 = 35/42 - 34/42 = 1/42;

14. 3/16 + 1/24 = 9/48 + 2/48 = 11/48;

15. 5/6 - 22/27 = 45/54 - 44/54 = 1/54;