We can make a string of equivalent ratios by continuing to scale up or scale down.
1 : 3 = 2 : 6 = 3 : 9 = 4 : 12 = 5 : 15 = 6 : 18 = 7 : 21....
All of these ratios show the same relationship.
Simplifying ratios to the simplest form can be helpful when solving problems that deal with ratios. You can simplify a ratio the same way that you simplify a fraction. This is basically just scaling down until you can no longer scale down anymore.