Ratios and Proportions

Definitions

• A proportion is two ratios that are equivalent

• A ratio is a comparison of two items

• Equivalent means equal

How do you write equivalent ratios?

1021

489

24

To check if 2 ratios are proportional…you can use cross

products or cross multiplying

5

2

10

4=

Is 2 x 10 equal to 4 x 5?If yes, you have a proportion!

You try it! Is this a proportion?

8

6

12

9=

You can also use “scale factor” to see if two ratios form a proportion

8

3249

=

x 3 =

x 3 =

Since 3 x 3 = 9 and 8 x 3 = 24, these ratios do form a proportion! 3 is called

the “scale factor”.

You Try it! Is this a proportion?

10

7

15

14=

You Try it! Is this a proportion?

5

12

15

36=

Homework:

P. 240 #1-9 all; 10-28 evens

Copy the proportions and show your work.