Mod 10 answers. This is the final answers only. For explanations of how to get them, see the extra explanation here

I always make a mistake somewhere, and this is a 1.0 draft of these answers. E-mail me if you find an error.

1. 8+7= 5

2. 3+9= 2

3. 6+7= 3

4. 3x6= 8

5. 4x8= 2

6. 7x9= 3

7. 2 - 8= 4

8. 4 - 6= 8

9. 5 - 8= 7

10. 6 + (3x8) + 9 = 9

(6+4+9=19=9)

11. 4x3 + 6 + 7x3 = 9

(12+6+21=2+6+1=9)

12. 4 - (3x9)= 7

(4-27=4-7=14-7=7)

13. 2 - (7x4)= 4

(2-28=2-8=12-8=4)

14. 0 - (4x8)= 8

(0-32=0-2=10-2=8)

Regular Polygons practice (For more details see explanation here)

15. Find the measure of an interior angle of a regular octagon (8-gon)

360/8=45; 180-45=135 The answer is 135°

16. Find the measure of an interior angle of a regular heptagon (7-gon)

360/7=51.43; 180-51.43=128.57. The answer is 128.57°

17. Find the measure of an interior angle of a regular dodecagon (12-gon)

360/12=30; 180-30=150; The answer is 150°