Ratio, Proportion, and Similarity
7-1 Ratio and Proportion
7-2 Properties of Proportions
Announcements
• You will have a new email account:– [email protected]– Password: maroons (you’ll need to change this)
• Next time we go to the lab that is what we will use. – I’ll send the assignment to that email.
• If you have a chance you can log in anytime and take the quiz on Classmarker.com– See me for a registration code if you didn’t get one
yet.
Ratio• One number divided by another
– Example: Boys to girls in this class?
– If there were no girls? • No Ratio (denominator can’t be 0)
• Ratios are usually expressed in simplest form.– Ex.
?
?
12 3
8 2?
What is the ratio of DI:IS?
0%
100%
0%
0%
0%
D
I
S
T
10
4
121. 6:5
2. 8:13
3. 5:8
4. 5:2
5. 8:7
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What is the ratio of IT:DS?
90%
0%
7%
0%
3%
D
I
S
T
10
4
121. 6:5
2. 8:13
3. 5:8
4. 5:2
5. 8:7
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Ratio (Continued)• Ratios can be used to compare more than
one thing:– Ex. a:b:c
The angles in a triangle are in the ratio 2:3:4. What are the angles?
0%
93%
0%
7% 1. 30, 60, 90
2. 20, 30, 40
3. 40, 60, 80
4. 60, 90, 120
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Proportions• An equation where
two ratios are equal– Ex. 3 1
a:b = c:d = 6 2
a c
b d
Properties of Proportions
a
b d
c MeansExtremes
Properties of Proportions• The product of the means equals the product
of the extremes
is equivalent t a bco = da
b d
c
Properties of Proportions• More Properties
is equivalent to:
ad = bc & = & = & =
a c
b d
a b b d a b c d
c d a c b d
If then which is correct?e g
f h
1. ef = gh
2. eh = fg
3. eg = fh
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SPICSA• Page 243-244 2-22 even
• Page 247 2-20 even
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