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### Course: Basic geometry and measurement>Unit 12

Lesson 2: Scale drawings

# Interpreting a scale drawing

Understand how a scale drawing is converted into real numbers using the scale factor. Created by Sal Khan.

## Want to join the conversation?

• i confused why it must be 1:80 can it be 80:1
• The ratio always comes in this order

Drawing to Reality

This means that for every 1 cm on the drawing, there is 80 cm in reality. To put it another way, take this

1:80 means that the building is 80 times the size of the drawing
80:1 means that the drawing is 80 times the size of the building

If it were 80:1, the drawing itself would be over 100m long.
• Couldn't you just leave it in centimeters?
• If you did, that would be hard to measure. So Sal reduced it to meters to make it "easier" to read
• I still don't get the meters part but I understand the centimeter part perfectly.
• Meters and centimeters are similar to feet and inches in the English system. There are 100 centimeters in every meter, just as there are 12 inches in every foot. The tricky thing is that there are 10,000 square centimeters in one square meter, and 144 square inches in one square foot.

Think of a floor tile that is one square foot. The width and height of the tile would both be 12 inches. Because the area of a rectangle = length * width, we would multiply 12 * 12 to get 144 square inches in that one square foot. I would recommend drawing it out for yourself if you still have trouble with that part.

If this didn't help, and you're still having trouble with this problem, let me know and I can try to find a better way of explaining it.
• This is the first video in this series, (Scale Drawings) and it operates through a ratio e.g. 1:80 But Sal never defines what either of these numbers are?? Which is which? I'm finding this very hard to understand despite the already present clarification on the video which states that the ration should be 1:80 not 80:1.

Sal still uses 80 in his multiplication and I am confused as heck as to what is what. I hope some good comes from this comment, cheers.
• It would be very inconvenient to draw things the same size they are in real life, so they are drawn smaller and the ratio is given.

1:80 just means that, for every unit in the drawing, there are 80 units in the real thing. Sal still multiplies by 80 because he interpreted the ratio the other way around, he read it as: for every 80 units in the house, there is 1 unit in the drawing. But, conventionally, the first number refers to the scaled version and the second number, to the actual thing.
• how can we measure the area with the help of scale
• Ok a blueprint example. Lets say 1 inch on the drawing is the same as 2 feet in the real world. So, what's the area of a room that is on the drawing 6 inches by 5 inches. Well convert to the real world area first, so 6 inches = 12 feet and 5 inches = 10 feet. Multiply 12 by 10 and the area of the room is 120 square feet.
• why is the bisector not parallel to the quadrant's perpendicularity
• It might be because of the hexagonoliar trignomotry.
• i dont get it at all , can you explain more?
• What do you not get about this? Sal is finding out the area of the drawing, and converting the area he just calculated to the area in the actual building.
(1 vote)
• why did they make the shape like that.