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# Ratios & Proportions

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on 29 September 2013

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#### Transcript of Ratios & Proportions

Ratios & Proportions
Units
Can you compare apples to oranges?
Writing Ratios
There is a specific way that you must write ratios
Ratio
A comparison between two numbers or items
2 girls
1 boy
4 apples
23 pieces of fruit
Proportion
- An equation containing two ratios that are equal

1
2
2
4
=
2:1
4:23
You can use Cross Multiplication to see if the two are proportional
1
3
9
3
3(3) = 1(9)
9 = 9
These ratios are proportional
So what happens when we don't know one of the numbers in a proportion?
x
4
12
16
=
What is the second key concept?
Hint...
Solve proportions by using Cross Multiplication
2 to 1
4 to 23
Three ways to express ratios:
1. Using the word "to"

2. Using a colon":"

3. As a fraction
Example:
Write the ratio of girls to boys in this classroom
Can you compare seconds to miles?
Proportions are always written using units of measurement that are of the same type
Examples:
Centimeters
Meters
Miles
Yards
Seconds
Minutes
Hours
Days
Cups
Pints
Gallons
Quarts
Pounds
Kilograms
Grams
Ounces
Weight:
Liquids:
Time:
Length:
1
3
3
9
=
=
?
?
Write the ratio of ties to bow ties
Now let's look at this proportion.....
x+3
2
=
15
6
4 fingers
2 hands
8 fingers
1 hand
=
must be in the same units
must be in the same units
Exit Slip
Compute the difference between the salaries from 1967 to 2010.
Write a reflection about the observation that you made
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