1. Which triangles are similar? 8 20 12 4 10 8
Which triangles are similar?
If they are in proportion they are similar.

2. Ch. 4-3 Solving Proportions

3. cross products
two products found by multiplying the denominator of each ratio by the numerator of the other ratio
20 = 6
90 = 90
6 = 9

4. proportion
an equation stating that two ratios are equal – use cross products to determine if a proportion or not
No, not a proportion
20 = 6
90 = 90
6 = 9
No, not a proportion
Yes a proportion

5. Example 1: Determine whether the following ratios form a proportion.
a.) b.)
Yes, because cross products are equal 60 = 60
No, because cross products are not equal 10 = 8

6. Example 2: Solve each proportion below by using the cross products.
a.) b.)
c.) d.)
Algebra Method:
2x = 90 Divide by 2 on both sides
x = 45
Algebra Method:
12x = 84 Divide by 12 on both sides
x = 7
Baby Math Method:
(9*10)/2
Baby Math Method:
(4*21)/12
Algebra Method:
15x = 180 Divide by 15 on both sides
x = 12
Algebra Method:
8x = 72 Divide by 8 on both sides
x = 9
Baby Math Method:
(12*6)/8
Baby Math Method:
(20*9)/15

7. Example 3: Set up a proportion for each scenario below and solve by doing the cross products.
a.) Andy paid $1.29 for 3 pieces of candy. At that rate, what would 8 pieces of candy cost?
b.) You are visiting friends in Estonia. Suppose the exchange rate is kroons = 1 dollar. How many Estonia kroons will you receive if you have $500?
x = $3.44
Dollars
Candy
Kroons
Dollar
x = $6340

8. #28 e.c. 4 pts. Show your steps for e.c.
Homework
Pg. 177
#6-26 even (just answer)
#28 e.c. 4 pts. Show your steps for e.c.