On a map with a scale 1:100,000, the distance between two cities is 12 cm. What would be the distance between these two cities on a different map with a scale 1:300,000?

The second scale is 3 times the first scale:

300, 000 / 100,000 = 3

Divide the distance by the same scale factor:

12 cm / 3 = 4 cm

Check:

The scale 1 / 100,000 means 1 cm = 1 km, so at 12 cm the cities are 12 km apart.

The second scale 1 / 300000 means 1 cm = 3 km, since the cities are 12 km apart, divide total distance by scale: 12/3 = 4 cm.