Download Proportions



An equation which shows two equivalent
ratios
They help us to find relationships in the real
world which are similar

Method 1 -- Scale Factor

Method 2 -- Cross Products

Step 1 – Setup the Problem
Julian is the best cake baker in Richmond. To make
a cake, he uses 1 egg for every 2 cups of flour. If the
recipe calls for 10 cups of flour, how many eggs does
he need?
Item
Ratio
eggs
1
X
flour
2
10

Step 2 – Find number (scale factor) that you can
multiply by to get from side with two numbers
to side with variable.
eggs
1
X
flour
2
10

Step 2 – Find number (scale factor) that you can
multiply by to get from side with two numbers
to side with variable.
x5
eggs
1
X
flour
2
10
x5

Step 3 – Multiple to find the answer
x5
eggs
1
X
flour
2
10
x5
2 x 5 = 10 and 1 x 5 = 5; therefore, X = 5

Step 1 – Setup the Problem
Tom is driving to New York. He travels 70 miles
every 2 hours. If the trip takes 8 hours, how many
miles will he travel?
Ratio
Miles
70
X
Hours
2
8

Step 2 – Multiple numbers from top left to
bottom right
Miles
70
X
Hours
2
8
70  8 = 560

Step 3 - Multiply numbers from top right to
bottom left
Miles
70
X
Hours
2
8
2 · x = 2x

Step 4 - Write products as an equation
Miles
70
X
Hours
2
8
560=2x

Step 5 – Divide by this number to get x by itself
560=2x
Wendy works at a kennel. There are 3 cats for every
2 dogs. If she takes in 18 cats, how many dogs will
she have?
Ratio
Cats
Dogs
Simone is taking a trip to Florida for spring break.
Her family travels 1250 miles in 25 hours. At their
rate of travel, how many miles did they travel per
hour?
miles
hours