* Find the 5 cm mark: This is the big number "5" on your ruler.

* Look at the smaller markings: Between each big number, you'll see smaller markings. These represent millimeters (mm).

* Count 5 millimeters: Since 0.5 cm is equal to 5 mm, count five of these smaller markings after the 5 cm mark. That's where 5.5 cm would be.

Here's a visual:

Imagine your ruler has these markings:

* 0 cm 1 cm 2 cm 3 cm 4 cm 5 cm 6 cm ...

Between the 5 cm and 6 cm marks, you'll have small lines representing millimeters. Count five of these lines after the 5 cm mark, and you'll find 5.5 cm.