Scale 1 : 20, 2.5 cm on the model

Step by step

The question

Question: with the scale 1 : 20, how long is 2.5 cm on the model for real?

The scale 1 : 20 means: 1 cm on the model is 20 cm for real.

Everything is 20 times bigger.

1 Multiply both sides

On the model we have 2.5 cm.

That is 2.5 times 1 cm.

So the real length is 2.5 times 20 cm too.

We multiply both sides by the same number, 2.5.

Forget the points: 20 times 25 is 500.

The numbers have 1 digit after the point.

So the answer has 1 too: 50.0, which is 50.

So the real length is 50 cm.

2 Check

Let's check: go back.

50 divided by 20 should give the model length, 2.5.

We get it again.

So 50 cm is right!

Let's look back.

First: multiply both sides.

Last: check.