Practice: Do all of these calculations mod 10 (* means multiply):

1. 8+7 ≡

2. 3+9 ≡

3. 6+7 ≡

4. 3*6 ≡

5. 4*8 ≡

6. 7*9 ≡

7. 2 - 8 ≡

8. 4 - 6 ≡

9. 5 - 8 ≡

10. 7 + (3*8) + 9 ≡

11. 4*3 + 6 + 7*3 ≡

12. 4 - (3*9) ≡

13. 2 - (7*4) ≡

14. 0 - (4*8) ≡

Find the missing number N in mod 10 arithmetic. If there is more than one answer, find all of the answers:

15. 3*N ≡8 (mod 10)

16. 3*N ≡4 (mod 10)

17. 3*N ≡1 (mod 10)

18. 7*N ≡3 (mod 10)

19. 7*N ≡8 (mod 10)

20. 2*N ≡6 (mod 10)

Do all of these calculations mod 7:

21. 6+4 ≡

22. 5+3 ≡

23. 4*6 ≡

24. 5*5 ≡

25. 3-6 ≡

26. 1-5 ≡

Do all of these calculations mod 8:

27. 7+4 ≡

28. 6*5 ≡

29. 4*7 ≡

30. 2-5 ≡