Step by step
The question
Question: with the scale 1 cm : 25 km, how long is 3 cm on the map for real?
map → real
The scale means: 1 cm on the map is 25 km for real.
1 cm → 25 km
1 Multiply both sides
On the map we have 3 cm.
That is 3 times 1 cm.
So the real length is 3 times 25 km too.
3 cm → 25 × 3 km
We multiply both sides by the same number, 3.
× 3 on both sides
25 times 3 is 75.
So the real length is 75 km.
3 cm → 75 km
2 Check
Let's check: go back.
75 divided by 25 should give the map length, 3.
75 ÷ 25 = 3
We get it again.
So 75 km is right!
Let's look back.
First: multiply both sides.
Last: check.
Answer
3 cm → 75 km