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## Topic D: Ratios of scale drawings

# Identifying scale factors

CCSS.Math:

## 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.