how do you do scale drawings?

Ex. Calgary is 3000km from Montreal. How far apart are they on a map with a scale of 1:25 000 000?

1mm represents 25 000 000mm

1mm represents 25 000 m

1mm represents 25km

$${\frac{{\mathtt{1}}}{{\mathtt{25}}}} = {\frac{{\mathtt{x}}}{{\mathtt{3\,000}}}} \Rightarrow {\mathtt{x}} = {\mathtt{120}}$$

that's 120mm = 12cm

does that make sense?