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Solve Proportional Relationships
CROSS PRODUCT RULE
In the proportion = , the cross products,
a · d and b · c are equal.
ab
cd
EX 1)= 2
412
44uses
1. Prove proportionality
EX 2) = 57
35
2521 2. Disprove proportionality3. Compare fractions
EX 3) 57
35
2521 <<
Use the cross products to solve proportions with variables. Which help you find missing values.
m = 3
Set up proportion.
Cross Multiply.
Divide by 15
= m5
915
EX 4) Step 1
Step 2
Step 39 x 5= 4545 ÷ 15
• Unit rate : a rate whose denominator is 1. It may not always look like a number; watch for words like per or each.
milesEX 5) 200 / 4 hours
How many miles traveled per hour?
Step 2: set up proportion=
Step 1: highlight rates
Miles Miles
Hours Hour
200
4
X1 Step 3: Cross multiply
and divide
200 X 1 = 200 ÷ 4 = 50 X = 50 mph
The ratio of students who ordered pizza to those that did not order pizza was 5 : 3. How many students would have pizza if 24 students ordered.
EX 6)
+ = not orderedordered Total ordered
=pizza pizza5
8 24
Xtotal total
X = 15
Sue needs 9 cups of flour to make 16 batches of cookies. How much flour does she need if she only wants to make a fourth of her recipe.
=cups Cups9
16 XX
batches batches4
9 X 4 = 36
36 ÷ 16 = 416 2 1
4 2 = Cups
EX 7)
A 12 oz sport drink cost $1.08 and a 16 oz. sport drink cost $1.28. Which drink is the better buy?
Step 2: set up proportion
=
Step 1: highlight rates
oz
$$
oz16
1.28 X1 Step 3: Cross multiply
and divide
EX 8)
Since you are comparing you will set up two proportions
=oz
$
oz12
1.08 X1
$
X = 0.09
X = 0.08The 16 oz. sport drink is the better buy?
Essential Question
How do you solve proportions?
Date _____________
Solve Proportional Relationships
CROSS PRODUCT RULE
In the proportion = , the cross products,
a · d and b · c are equal.
ab
cd
EX 1) uses1.
EX 2)
2. 3.
EX 3)
You can use the cross product rule to solve proportions with variables. Which help you find missing values.
=
=
1.
2.
3. =
EX 4)
How many miles traveled per hour?
miles
• Unit rate : a rate whose denominator is 1. It may not always look like a number; watch for words like per or each.
EX 5) / hours
Step 2:
=
Step 1:
Step 3:
The ratio of students who ordered pizza to those that did not order pizza was : . How many students would have pizza if students ordered.
EX 6)
+ =
=
Sue needs cups of flour to make batches of cookies. How much flour does she need if she only wants to make a fourth of her recipe.
=
EX 7)
A 12 oz sport drink cost $1.08 and a 16 oz. sport drink cost $1.28. Which drink is the better buy?
=
EX 8)
=
Essential Question
How do you solve proportions?
