500 in 2:3 is saying that there are five different parts (2 + 3)
This means that 500 needs to be split into five, which is 100.
After that all you need to do is put 2 'sections' on one side and 3 on the other.
For example, 2 : 3 = 2( x 100) : 3( x 100)
= 200 : 300