Ratios

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# Ratios - PowerPoint PPT Presentation

Ratios. Compare the number of boys to girls in the class. Free powerpoints at http://www.worldofteaching.com. The number of boys = The number of girls = If we compare boys to girls we get ___ boys to _____ girls. What do we call a comparison between two or more quantities?.

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## PowerPoint Slideshow about 'Ratios' - kelton

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Presentation Transcript
Ratios
• Compare the number of boys to girls in the class.

Free powerpoints at http://www.worldofteaching.com

The number of boys =
• The number of girls =
• If we compare boys to girls we get

___ boys to _____ girls.

What do we call a comparison between two or more quantities?

We just found the RATIO of boys to girls.

RATIO

Is the ratio of girls to boys the same ?

No, when writing a ratio, ORDER matters.

AIM:

What is a ratio?

The ratio of girls to guys is 2 to 12.

Would you want to attend the party?

How many basketballs to footballs are there?
• For every 4 basketballs there are 6 footballs.
• The ratio is 4 to 6.
What are some other ways we can write the ratio of basketball to footballs?
• 4 to 6
• 4 : 6
• 4

6

Every ratio can be written in 3 ways:

First quantity to Second quantity

Careful!!

Order matters in a ratio.

4 to 6

Is NOT the same as

6 to 4

First quantity : Second quantity

First quantity divided by the second quantity (as a fraction).

• 6:8 , 6 to 8, and 6

8

Since a fraction can be simplified, We can simplify the ratio 6/8 to 3/4. The ratio of sandwiches to coke bottles can also be expressed as 3 : 4 or 3 to 4.

In other words, ratios can be simplified to form equivalent ratios.

Equivalent Ratios
• = 4 / 4 = 1 = 1 to 2
• 8 8 / 4 2
• Simplify the following ratios:
• 4 to 8
• 10 to 8
• 8 to 10

GCF = 4

Step 1 – Write the ratio as a fraction

Step 2 – Simplify the fraction (Find the greatest common factor (GCF) of both numbers and divide the numerator and denominator by the GCF).

Step 3 – Write the equivalent ratio in the same form as the question

• For example, the ratio 2 : 3 can also be written as
• 4 : 6 (multiply original ratio by by 2)
• 6 : 9 (multiply original ratio by by 3)
• 8 : 12 (multiply original ratio by by 4)
• The ratio 2 : 3 can be expressed as
• 2x to 3x (multiply the original ratio by any number x)
Compound Ratios
• A ratio that compares more than 2 quantities is called a compound ratio.
• Example:
• A cake recipe says the ratio of cups of milk, sugar, and batter are 1:2:4.
• This means that there is one cup of milk for every two cups of sugar and four cups of batter.
A bag contains 18 yellow, blue, and red marbles. The ratio of yellow to blue to red marbles is 4 : 2 : 3.
• Write the ratio of yellow to blue marbles in simplest form.
• What is the ratio of yellow to red marbles?

4 : 2 can be simplified to 2 : 1

4 : 3

Practice problem # 1

(1) You have 100 different shirts. The ratio of blue to black shirts is 20 .

30

a) Write the ratio of blue to black shirts 3 different ways.

b) Write the ratio in simplest form.

c) Explain what this ratio tells us.

d) How many black shirts do you have?

Solution - # 1 

You have 100 different shirts. The ratio of blue to black shirts is 20 / 30

a) Write the ratio of blue to black shirts 3 different ways.

20 to 30 , 20 : 30, 20

30

b) Write the ratio in simplest form.2

3

c) Explain what this ratio tells us. For every two blue shirts, there are 3 black shirts.

d) How many black shirts do you have?

2x + 3x = 100

5x = 100

x = 20

There are 2x black shirts so 2 (20) = 40 black shirts

Practice Word Problems
• You go to a party where the ratio of boys to girls is 28 to 56. Express the ratio of boys to girls in simplest form.
• Explainwhat this ratio tells us.
• 28 / 56 = 1 / 2
• The ratio of boys to girls is 1 to 2
• (2) For every 1 boy there are 2 girls at the party.
Practice Word Problems
• Mindy has 72 candy bars. If the ratio of Mars to Snickers is 8:4, Find the number of each type of candy.
• Explain what this ratio tell us.
Challenge Question
• The perimeter of a rectangle is 500 feet. The ratio of the base and height is 3:2. What is the measure of the height?