Ratio, Proportion, and Similarity

7-1 Ratio and Proportion

7-2 Properties of Proportions

Announcements

• You will have a new email account:– firstname@hohmanprovement.com– 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