Map scale 1 cm : 15 km, 4.2 cm on the map

Step by step

The question

Question: with the scale 1 cm : 15 km, how long is 4.2 cm on the map for real?

The scale means: 1 cm on the map is 15 km for real.

1 Multiply both sides

On the map we have 4.2 cm.

That is 4.2 times 1 cm.

So the real length is 4.2 times 15 km too.

We multiply both sides by the same number, 4.2.

Forget the points: 15 times 42 is 630.

The numbers have 1 digit after the point.

So the answer has 1 too: 63.0, which is 63.

So the real length is 63 km.

2 Check

Let's check: go back.

63 divided by 15 should give the map length, 4.2.

We get it again.

So 63 km is right!

Let's look back.

First: multiply both sides.

Last: check.