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## 7th grade (Eureka Math/EngageNY)

### Course: 7th grade (Eureka Math/EngageNY) > Unit 1

Lesson 4: Topic D: Ratios of scale drawings- Exploring scale copies
- Explore scale copies
- Corresponding points and sides of scaled shapes
- Corresponding sides and points
- Identifying scale copies
- Identify scale copies
- Identifying scale factors
- Identify scale factor in scale drawings
- Identifying values in scale copies
- Scale drawing: centimeters to kilometers
- Making a scale drawing
- Construct scale drawings
- Interpreting a scale drawing
- Solving a scale drawing word problem
- Scale drawing word problems

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# Identifying scale factors

CCSS.Math:

Sal looks at a figure and a scale copy of the figure to determine what scale factor was used to create the scale copy.

## Want to join the conversation?

- Is the scale factor 1:3? I think I'm right, but I'm not sure.(6 votes)
- no the scale factor is only 3(12 votes)

- I didn't get why it was 4, 6.5 , and 12. Isn't the scale factor suppose to be less than one?(7 votes)
- No, if a Scale Factor is less than 1, you will be shrinking a shape. If it is greater than 1, it will be expanding.(2 votes)

- how do you do the videos(4 votes)
- You click on the big triangle that should pop up.(5 votes)

- what if you have a question like "Tommy drew a scale drawing of a house and its lot. He used the scale 7 centimeters = 2 meters. What is the drawing's scale factor?". How would you solve it?(3 votes)
- Well, we should convert meters to centimeters first. 7 centimeters -> 200 centimeters (2 meters), so the scale factor is 200/7.(4 votes)

- with the first example i am confused. if figure b side is 6 and figure a side is two , how is it scale up by 3? i'm not understand how he got the 3. to go from 2 to 6 is four(4 votes)
- great video, but how would you decide between the three options left at the end, saying that your problem is not a multiple choice but a direct answer how would you finish solving that?(3 votes)
- If it was not multiple choice, you could say that it is <16. Or they might provide you more information to enable you to completely solve it.(2 votes)

- What if the figures are triangles?(3 votes)
- I don't understand how we are looking for a scale less than one, then we are looking for answers less than 16. Does less than one mean the scale will just be smaller? I am missing something.(3 votes)
- What do I do when a scale factor is a fraction?(2 votes)
- I know this is a year late to your question Jordan, but a scale factor is the number multiplied to a side length to equal the similar figure.(2 votes)

## Video transcript

- [Instructor] So right over here, Figure B is a scaled copy of Figure A and what we wanna do is figure out what is the scale factor to
go from Figure A to Figure B? Pause the video and see if
you can figure that out. Well, all we have to do is
look at corresponding sides and think about how much
they have been scaled by. So for example, this side right over here would correspond to this side
right over here on Figure B and over here, it had length two and over here, it has length one, two, three, four, five, six. So it looks like that
side has been scaled up by a factor of three and so if Figure B truly is a scaled copy then every side should be
scaled up by a factor of three and we could verify that. We don't have to do it with every side. We're being told that
these are scaled copies but we can see that this is the case. For example, this side right over here corresponds to this base right over here. This has length three. So if we're scaling up
by a factor of three, we should multiply that by three and this should be of length nine. Let's see if that's the case. One, two, three, four, five,
six, seven, eight and nine. And so you can see we can feel pretty good that Figure B is a scaled copy of Figure A and that scaling factor is three. Let's do another example. So here, we are told
Ismael made a scaled copy of the following quadrilateral. He used a scale factor
less than one, alright, and then they say what could be the length of the side that corresponds to AD? So AD is right over here. AD has length 16 units in
our original quadrilateral. What could be the length of the side that corresponds with AD on the scaled copy of the quadrilateral? So it's a scale factor less than one. So we're gonna get something
that is less than 16 for that side and the rest of it will all
be scaled by the same factor. So the resulting quadrilateral
might look something, might look something like this. This is just my hand-drawn version. So the key realization is is if our scale factor is less than one, this thing right over here is going to be less than 16 units. So let's look at the choices and it says choose three answers. So pause the video and
which of these would match if we're scaling by a
factor of less than one? Well, we just have to see which of these are less than 16 units. This is less than 16. This is less than 16. This is less than 16 and those are the only
three that are less than 16. 32 units, this would be
a scale factor of two. 64 units, this would be
a scale factor of four. Clearly a scale factor
that is not less than one.