Math answers p. 401

3. 3/4

4. 5/6 

5. 6/7

6. 5/8

7. 8/9

8. 8/10, reduced to 4/5.  

You can divide 8 and 10 by 2.  8 divided by 2 = 4   AND   10 divided by 2 = 5

9. 9/12, reduced to 3/4

You can divide 8 and 10 by 3.  9 divided by 3 = 3  AND   12 divided by 3 = 4

11. 5/10 + 2/10 = 7/10
There were 10 squares in all. Ten is the denominator.
Five are blue.  5/10
Two are purple. 2/10

13. 2/5 + 2/5 = 4/5