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# Copy of Ratios & Proportions

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by

## Suzanne Dobson

on 23 July 2014

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#### Transcript of Copy of Ratios & Proportions

solve??
Step 1
2. Cross multiply
3. Isolate the variable
Ratios & Proportions
First,
A comparison between two or more numbers or items
2 boys
3 girls
Proportion
- An equation containing two ratios that are equal

=
2:3
4:20
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
=
1. Set up a proportion
3 steps...
SWBAT use
cross multiplication
in order to
solve proportions
2 to 3
4 to 20
Three ways to express ratios:
1. Using the word "to"

2. Using a colon":"

3. As a fraction
=
?
?
What is the ratio of ties to bow ties?
Now let's look at how to set up a proportion.....
=
5 fingers
2 hands
10 fingers
1 hand
=
must be in the same units
must be in the same units
What if....
How many fingers compared to
how many hands
5 fingers
1 hand
What if we ride bikes for
40 minutes and make it
5 miles...how long would
we make it if we rode for
60 minutes?

You are thinking...
I can't do that!
It's too hard.
Yes u can!!
What are the quantities we are comparing?
miles to minutes
miles : minutes
miles
minutes
Find an equal ratio
5 miles to 40 minutes = x miles to 60 minutes
5 miles : 40 minutes = x miles : 60 minutes
5 miles
40 min
x miles
60 min
=
Cross multiply
means
extremes
5

x
40

60
=
5 (60)
300
40 (x)
40(x)
300
=
40(x)
We need to isolate the variable...
big words for get the variable (x) by itself.

What is the opposite of multiplication?
DIVISION
300 = 40 (x)
To get the "x" isolated, divide
each side by 40
300
40
7.5!
We can ride
7.5 miles in
60 minutes
When you put it all together...
5 miles
40 minutes
x miles
60 minutes
=
Extremes
5(60) = 300
Means
40(x)
40(x) = 300
40(x) 300
40 40
Step 1
Set up the proportion
Step 2
Multiply
means x extremes
Step 3
Isolate the variable
=
x = 7.5
Miles on top
minutes on bottom
Next
we defined
PROPORTION
1
3
3
9
Check - is it equal?
means 3 x 3 = 9
and
extremes 1 x 9 = 9
Yes
9 = 9 It
is
a proportion!
2:6
2 to 6
2 choco
package
Gage
Veronica
Zanyah
Seanterria
Aron
40x
40
7.5 =

x
=
=
300
=
40x
Our proportion is...
5 miles 7.5 miles
40 minutes 60 minutes
=
we defined "Ratio"
3 to 16
3:16
3 orange
16 total m&ms
Domne't
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