This document defines ratios and proportions. A ratio compares two numbers using a colon, like 2:5 which reads as "2 to 5". A proportion sets up an equality between two ratios using a colon for each term, like a:b = c:d. To check if two ratios are equal, you calculate the cross product - if the products are the same, the ratios are equal. Proportions can be used to solve for unknown values. Examples provided demonstrate using ratios and proportions to solve word problems involving comparisons of amounts.

1. Ch.7.1_RatiosAndProportions.notebook January 04, 2012
Chapter 7.1
Ratios and Proportions

2. Ch.7.1_RatiosAndProportions.notebook January 04, 2012
Ratio: a comparison of two numbers
2
2:5 2 to 5
5
Proportion: an equation that sets 2 ratios
equal to each other.
a:b = c:d
a c Extremes
=
b d Means
2 4
=
5 10
If 2 ratios are the same, then their cross products
will be equal.
EX: Are 5:6 and 10:12 equal ratios?
5 10
6 12
EX: Are 65:11 and 31:5 equal ratios?
The cross products will be equal in a proportion.
EX: Solve for y
2 =5
3 y

3. Ch.7.1_RatiosAndProportions.notebook January 04, 2012
Examples
A juice recipe calls for 3 parts pineapple juice
to 5 parts orange juice. How much pineapple juice
should be added to 16 L of orange juice?
The ratio of adults to children is 2:15.
There are 102 total people, how many are adults?
A gas station charges $3 for 2 sodas. How much
money would 5 sodas cost?
2 people are splitting the cost of a used car in the ratio
4:5. The total cost of the car is $3,150. How much does
each person pay?