To get a number in a ratio, add up the two numbers in the ratio:
In this case add up 5 and 8 to get 13 parts.
If 52 is split into 13 parts each part is:
52/13 = 4
We then multiply the number of each part by the total for each side of the ratio so:
5 x 4 = 20
8 x 4 = 32
So the answer is 20:32
We can check by adding the ratio up to see if we get our original number, which we do.