Exercise 1 solution

Ground distance = map distance x scale number, then convert units.

6 cm on 1:25,000: 6 x 25,000 = 150,000 cm = 1,500 m = 1.5 km
6 cm on 1:50,000: 6 x 50,000 = 300,000 cm = 3,000 m = 3.0 km
3.2 cm on 1:50,000: 3.2 x 50,000 = 160,000 cm = 1,600 m = 1.6 km

Why the first two differ: the same 6 cm covers twice as much ground on the
1:50,000 map, because each centimetre stands for 500 m instead of 250 m.
Checks: at 1:25,000, 4 cm = 1 km (so 6 cm = 1.5 km); at 1:50,000, 2 cm = 1 km
(so 6 cm = 3 km and 3.2 cm = 1.6 km).