Question

1) In the national park, the ratio of black bears to grizzly bears is 3:1.

Answer 1

A)
3 : 1
24 : ? 
Add the ratio together (3+1=4), Divide the one you know (24 Black bears) by the ratio (24/4=8), the answer equals the amount of the missing value. (?=8)

B)
3 : 1
? : 12
12*3=36    ?=36
The black bear is just 3* bigger than the grizzly bear.

C)
Total =20
Add the ratio together (3+1=4), divide by the total (20/4=5), and then just multiple the ratios by 5.
3 : 1
15 : 5

I hope this helps :)