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## 7th grade

### Course: 7th grade > Unit 8

Lesson 2: Scale drawings- Scale drawings
- Scale drawing: centimeters to kilometers
- Scale drawings
- Interpreting a scale drawing
- Scale drawing word problems
- Creating scale drawings
- Making a scale drawing
- Construct scale drawings
- Scale factors and area
- Solving a scale drawing word problem
- Relate scale drawings to area

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# 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(69 votes)
- 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.(39 votes)

- Couldn't you just leave it in centimeters?(32 votes)
- If you did, that would be hard to measure. So Sal reduced it to meters to make it "easier" to read(24 votes)

- I still don't get the meters part but I understand the centimeter part perfectly.(4 votes)
- 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.(19 votes)

- 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.(6 votes)- 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.(12 votes)

- why is math so boringgggg(8 votes)
- you mean.......just you? not for all.(3 votes)

- how can we measure the area with the help of scale(5 votes)
- 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.(6 votes)

- why didn't we divide 128,000 by 80?(4 votes)
- If we do that, it would be the size of the living room on the floor plan*80 or the size of the living room in the real world/80.(2 votes)

- why is the bisector not parallel to the quadrant's perpendicularity(4 votes)
- It might be because of the hexagonoliar trignomotry.(2 votes)

- i dont get it at all , can you explain more?(4 votes)
- 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.(2 votes)

- I dont get the house assumption(3 votes)
- Yes, He also calculated the perimeter of the rooms in feet.(3 votes)

## Video transcript

Maya and Mabel are
inspecting a 80 to 1 scale floor plan
of their new house. The dimensions of the living
room in the scaled plan are 4 centimeters by 5
centimeters right over here. What is the area of the
living room in the real world? So they gave us these
dimensions right over here. This is the scale
plan, and then we could figure out these
dimensions in the real world by looking at the scale
factor right over here. It's an 80 to 1
scale floor plan. And we can assume
that the house is much bigger than the floor plan. So the 80, for every
80 units in the house, that represents 1 unit
on the floor plan. So if we had 80
meters in the house, that would be represented as
1 meter on the floor plan. If we had 80 centimeters
in the house, that would be represented by 1
centimeter in the floor plan. And it goes the
other way around. 1 centimeter on the
floor plan would represent 80 centimeters
in the house. And it's always important to
do-- if this confuses you, just always do a reality check
that the house should be bigger than the floor plan. So if the floor plan for this
dimension of our living room is 4 centimeters, the actual
house will be 80 times that. And 80 times 4 is 320-- let
me do that in a blue color-- is equal to 320 centimeters. And we can do the same thing for
the length of the living room. So 80 times 5
centimeters is going to get us to-- is going to be--
80 times 5 is 400 centimeters. So we could figure out
the area of this room in centimeters, if we
like, and I guess, why not? It might be easier to
convert it to meters later. So let's see, 400 centimeters
times 320 centimeters. Let me write this down. 400 times 320. Let's think about it. 4 times 32 is going to
be 120, plus 8, 128. And I have 1, 2, 3 zeroes. 1, 2, 3. So it's going to be 128,000
centimeters squared. Now that's a lot of
square centimeters. What would we do if we wanted
to convert it into meters? Well, we just have to figure out
how many square centimeters are there in a square meter. So let's think
about it this way. A meter is equal to-- 1 meter
is equal to 100 centimeters. So a square meter, so
that's right over there. 1 meter squared would be
1 meter by 1 meter, which is the same thing as 100
centimeters by 100 centimeters. And so if you were to calculate
this area in centimeters, 100 times 100 is 10,000, is
equal to 10,000 centimeters squared. So you have 10,000
square centimeters for every square meter. And so, if you want to convert
128,000 centimeters squared to meters squared, you
would divide by 10,000. So dividing that by 10,000 would
give us 12.8 square meters. Now, another way you
could've done it, and maybe this would
have been easier, is to convert it up here. Instead of saying
400 centimeters times 320 centimeters,
you would say, well, 400 centimeters, that's
going to be 4 meters. And 320 centimeters,
well, that's 3.2 meters. And you would say,
OK, 4 times 3.2, that is 12.8 square meters. But either way, the
area of the living room in the real world in meters
squared, or square meters, is 12.8.