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# Download Unit 3: Ratios and Proportional Relationships

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```Real world Problems
There are examples of finding the cost of flooring using proportional relationships
and given information.
There are questions like using proportions to modify a recipe to create a different
number of servings.
The next unit is about percentages and will go in depth with percentage problems. In
this unit we will âplant the seedâ on discounts, markups and changes based on
fractions. This will then tie into the percentages for the next unit.
Scale Drawings
Scale drawings are reductions or enlargements of a two-dimensional picture. The
dimensions from the original to the scale drawing are proportional and have a scale
factor. The scale factor is a constant of proportionality.
Scale Drawings
When the units are the same:
The scale factor is the same as the constant of proportionality.
ððð¤
= ð ðððð ðððð¡ðð
ðððððððð
When the scale factor is greater than one, it is an enlargement.
When the scale factor is less than one, it is a reduction
When the units are different:
The scale is a ratio. i.e. 1 in. = 4 ft. You set up proportions to find the missing length.
For example: 2 Â½ in = _____ft.
1
2 2 ðð
ð¥ ðð¡
=
1ðð
4ðð¡
Method 1: You multiply 1 x 2 Â½ to get 2 1/2 , so multiply 4 x 2 Â½ to get 10ft.
Method 2: Use cross products (multiplication) to get the answer.
1
2
2
ð¥
=
1
4
1(x) = 2 Â½ (4)
X = 10
```
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