1) in the national park, the ratio of black bears to grizzly bears is 3: 1.
a)if there were 24 black bears, how many grizzly bears would there be?
b)if the park had 12 grizzly bears, how many black bears would it have?
c) if the total of black & grizzly bears was 20. how many black bears & how many grizzly bears would it have? bears, grizzly bears.

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 :)