A map is drawn to a scale of 1 : n.
The actual distance between two points X and Y is 2.8 km.
On the map, they are 4 cm apart. Find the value of n. Answer n = ...

1. Convert the actual distance to centimetres.

$2.8\text{ km} = 2.8 \times 1000 \times 100\text{ cm} = 280000\text{ cm}$

2. Form the scale ratio and find the value of $n$.

Map : actual $= 4 : 280000$

Divide both parts by $4$:

$4 : 280000 = 1 : 70000$

So $n = 70000$.