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Scale drawing: centimeters to kilometers

Sal uses ratios to figure out how far apart two cities should be on a map. Created by Sal Khan.

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Video transcript

The scale on a map is 7 centimeters for every 10 kilometers, or 7 centimeters for 10 kilometers. If the distance between two cities is 60 kilometers-- so that's the actual distance-- how far apart in centimeters are the two cities on the map? Well, they give us the scale. For every 10 kilometers in the real world, the map is going to show 7 centimeters. Or another way to think about it is if you see 7 centimeters on the map, that represents 10 kilometers in the real world. Now, they're saying that the distance between two cities is 60 kilometers. So it's essentially 6 times 10 kilometers, so times 6. So if you have to 6 times 10 kilometers on the map, you're going to have 6 times 7 centimeters, so times 6. And 6 times 7 centimeters gets you to 42 centimeters. So how far apart in centimeters are the two cities on the map? Well, 42 centimeters.