Examples: 12 out of 20, 12 boys and 8

girls

What are some ways you can compare the number of boys to total students in this classroom?

Ratios and Rates

A ratio is a mathematical way to compare two

quantities…you can compare part to partIn our example boys to

girls…you can compare part to wholeIn our example boys to

total

In our example total to girls

…you can compare whole to part

A ratio can be written in 3 ways:

12 to 20

A ratio can be written in simplest form just like a

fraction

examples:

30

4

km

hr

A rate is a comparison of two quantities using different units

30

$15

kg

A unit rate is a rate where the denominator is one unit

7.5

1

km

hr10 / secmexamples

:

How do you change a rate into a unit rate?

30

4

km

hrlook at our previous example:

One method Divide the numerator by the

denominatorWhich is the same as

Dividing both the numerator and denominator by 4

Let’s practice on whiteboards

Try changing these to unit rates

Typing 300 words in 6 minutes Running 15 km

in 45 minutes

Solving 20 math problems in 30

minutes

Let’s see what happens to these “units” when solving a

problemLuke texts 25 words/minute.

How many words can he text in 30 minutes?

Pete drives at a speed of 50 kilometers per hour. How far

will he go in 4 1/2 hours?

Katie counted 24 petals on one of the dozen roses that her

boyfriend gave her. About how many petals would there be on

all the roses together?

Using unit rates is a good way to compare…

Which is the better price?

$6.25 for 25 oranges or $7.20 for 30 oranges?

You can find unit rates in different ways…

In a table From a graph

From an equationM = 55G