# Lesson: Scale Factor

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### Lesson Objective

We will be able to determine scale factor.

### Lesson Plan

Do Now: (5 minutes)

1) A map has a scale of 1 inch = 3 miles. If two cities are 4 ½ inches apart on the map, what is their actual distance from each other?

2) Stamps are \$2.40 for 20 of them. Find the unit rate.

3) Evaluate 6x² if x = 4

Direct Instruction: (20 minutes)

Yesterday we solved problems that involved scale. Why do we use scales? What did we need to know in order to solve the problems involving scale?

Today we are going to take a look at finding the scale factor for models or maps.
Have students generate examples of ratios that could be scales.
Show students examples of scale factors. What is different between what we have for scales and what we have for scale factors? Generate definition of scale factor.

Scale factor- a scale written as a ratio without units in simplest form.

How do you think we eliminate the units?  Let's take a look at how it works.
Ex. Find the scale factor of a model sailboat if the scale is 1 inch = 6 feet.
-          Convert feet to inches
-          Divide out the common units.

Ex. What is the scale factor of a model car if the scale is 1 inch = 2 feet?

To find scale factor:
- Convert the scale to the same unit
- Reduce and cancel the units.

Guided Practice: (10 minutes)
Find the scale factor for the following scales:
2inches = 15 feet
1 in = 20 yards
0.5 cm = 1.5 m
1 in = 0.5 in

Assessment: (10 minutes)
Scale factor work-out

### Lesson Resources

 scale factor assessment   Assessment 1,703