Answer:
6. integer, natural number
7.No
8. 6, 5.7
17. a=5
18.yes
19.yes
20.yes
explaination for 18-20: They all can be put into a fraction. For 18, after rooting both numbers, would be 1/3 (same with 20). For 19, it would be root 5 over 3.
Step-by-step explanation:
