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### Course: 7th grade (Illustrative Mathematics)>Unit 1

Lesson 6: Lesson 7: Scale drawings

# Scale drawings

Sal finds a missing side length in a scale drawing when given either a set of corresponding side lengths or one side length and the scale factor.

## Want to join the conversation?

• This kind of feels over complicated, this is a very simple thing.
• I know right?! but it was still pretty helpful once i understood what they meant
• my name is Bella btw I need help, I'm only 12 and in 7th grade;-;
• Hi Bella! Maybe this can help:

A scale drawing is a drawing of an object that is larger or smaller than, but proportional to, the original object.

If the scale drawing is larger than the original object, then it is called an enlargement.

If the scale drawing is smaller than the original object, then it is called a reduction.

A scale is a ratio of a length in the drawing to the corresponding length in the actual object.

You can write a scale in three ways: as a ratio, as a fraction, or with an equal sign:

*drawing length : actual length

drawing length / actual length

drawing length = actual length

To find the scale used in a drawing or model, divide the drawing length by the actual length. Then write the ratio in simplest form.

Hope this helps!
• Sal knows math, but not chickens. That my friends, is a Rooster.
• belly laughs for infinity
• explain a little more about it
• I kinda get it but not much
• how do i solve it
• Could you also divide and get the same answer or does it have to be multiplied?
• try it yourself to see if it does work. both ways I mean.
• how do i sumbmit this?
• this was a little confusing at first
• But do you get it now? If not, I can help you.
• This question stumped me. I tried using every source of help I could find for this equation, and nothing. The question: The scale for the drawing of a rectangular playing field is 2 inches = 5 feet. Find an equation you can use to find the dimensions of the actual field. What are the actual dimensions? Btw, length is 20in and width is 10 in.
• you should make a proportion that says
2"/5'=20"/L' and another that says 2"/5'=10"/w'
"L" would equal 50' and "w" would equal 25'

key for symbols incase u don't understand what I said
" = inches
' = feet
L = length
w = width

## Video transcript

- [Instructor] We're told a scale on a blue print drawing of a house shows 10 centimeters represents 2 meters. What number of actual meters are represented by 18 centimeters on the blue print? So pause this video and see if you can figure it out. So the main thing to realize is that a blue print drawing is a scale drawing of something in the real world. In this case of a house. And so what we can do is set-up a little bit of a table here, so let's put the drawing on the left, so this is the blue print drawing. And then this is the real world. Real world on the right. And the unit that we're using, the units that we're using in our drawing are centimeters. So we have centimeters over here. And then the real world, we're thinking in terms of meters. And so let me make a little bit of a table. And so we see that 10 centimeters on the drawing corresponds to 2 meters in the real world. So 10 centimeters in the drawing, corresponds to 2 meters in the real world. Then they ask us what number of actual meters are represented by 18 centimeters on the blue print? So 18 centimeters on the blue print would correspond to what in the real world? Well there's several ways to approach it. One way to think about it is, look to go from 10 to 18, we are going to multiply by 1.8. So to go from what 10 centimeters represents in the real world to what 18 centimeters represents in the real world, you would similarly multiply by 1.8. So times 1.8, which would give us 3.6. 3.6 what? 3.6 meters in the real world. So 3.6 meters in the real world would be what 18 centimeters on the blue print represents. Let's do another example. Jaylynn draws a hen with a scale of 2 units on her graph paper represents 6 meters, 6 centimeters in the real world. The hen is 16 units tall in the drawing. What is the height in centimeters of the actual hen? So once again, pause this video and see if you can figure that out. Alright, so let's just set-up our tables again. So for our table, so we have our drawing, and then we have the real, real world. And in our drawing, it's just these little units on our graph paper, so I'll call it just that, units. And the real world, we're thinking in terms of centimeters, centimeters. And so let me set-up a little bit of a table here, and so we know, and we see that right over here from this scale. We can see two units represent 6 centimeters in the real world. So two units in our drawing represent six centimeters in the real world, and then they say the hen is 16 units tall in the drawing. So it's 16 units tall in the drawing. What would that represent in the real world which would be the actual height of the hen? If two units represent six centimeters, and now we have eight times as many units, well that's gonna represent eight times as many centimeters. So six times eight is 48 centimeters. So what is the height in centimeters of the actual hen? 48 centimeters, 48 and we're done.