1. Today’s Lesson: Scale proportions What: Why:
. . . so I can use proportions to solve problems involving scale drawings.

2. What is the method we practiced for setting up proportions involving scale drawings?

3. Vocabulary:
scale drawing/model — represents something that is too ______________ or too _______________ to be drawn at actual size.
scale factor-- gives the ratio of the paper measurement to the________________ measurement (If the scale is 3 cm = 9 mi., then the scale factor is )
small
LARGE
real-life

4. real-life 0.5 𝑖𝑛 20 𝑚𝑖 = unknown 𝒙 𝟓𝟎 𝒎𝒊
How to solve a scale drawing problem using a proportion:
Step One: Set up given map/ blueprint scale as a ratio with paper measurement on top and ____________________ measurement on the bottom.
Step Two: Set up other side of proportion by placing what you know (as given in problem) in the correct position (paper on top and real-life on the bottom). “x” goes in the remaining spot (represents the __________________________).
Example:
A certain map has a scale of ½ inch = 20 miles. If two towns are 50 miles apart, how far apart are they on the map?
0.5 𝑖𝑛 20 𝑚𝑖 =
x = 1.25 in
Note: The following is not the only way to set up a scale proportion, but it is the way we will use in order to be consistent!
real-life
unknown
𝒙 𝟓𝟎 𝒎𝒊
Start with the SCALE– given in the problem!
What else does the problem already tell us?? =
20x 20 20

5. x = 50 ft Blueprint Examples: Scale: 2 cm = 5ft Together:
If a room is 20 cm in length on the
blueprint, what is its actual length?
x = 50 ft

6. Blueprint Examples:
On your own:
Scale: 𝟏 𝟒 in = 2 ft
If a room is 20 ft long in real-life, what is
its length on the blueprint?
x = 2.5 in

7. Map scenarios:
Together:
Scale: 2cm = 9 km
If two towns are 56 km apart in real-life,
how far apart are they on the map?
x ≈ 12.4 cm

8. Map scenarios:
On your own:
Scale: in = 20 mi
If the distance between two towns on
the map is 2 in, how far apart are they
in real life?
x ≈ miles

9. What is the scale?
Together:
The distance from Pleasantville to Jefferson
is 25 miles, but measures 2.5 cm on the map.
What is the map’s scale?
1cm = 10 miles

10. What is the scale?
On your own:
The kitchen is 3 cm in length on the blueprint,
but measures 15 ft in actual length. What is the
blueprint’s scale?
1 cm = 5 ft

11. Wrap-it-up/summary: What is the method we practiced for setting up
proportions involving scale drawings?
Write the given scale as a ratio– paper on top,
real-life on bottom. Set up the “known” in the
correct spot on other side– show the labels!!

12. END OF LESSON