You don't say what you are measuring.
Generally, questions like this do include that info.
Example: What is the unit rate of (1/5) white per (1/4 yellow)?
To determine this, divide (1/5) white) by (1/4 yellow)
1 white
-----------
5
------------------ = 0.20/0.25 white per yellow, or 0.8 white per yellow.
1 yellow
-----------
4