|
TUTORIALS:
|
Ratios and Proportions
A ratio is a way to compare two quantities using division.
Ratios are often written as fractions.
For example:
• If a class of 24 students contains 11 women and 13 men, then the ratio
of women to men is 11 to 13, which we can write as
 .
• If 10 pounds of watermelon costs $3, then the ratio of cost to weight is
 .
A proportion is an equation that sets one ratio equal to another ratio.
Definition —
Proportion
A proportion is an equation that can be written in the form
Here b ≠ 0 and d
≠ 0.
Here’s a problem we can solve with a proportion.
If an 18-pound melon costs $3.60, what is the cost of a 26-pound melon?
| If we assume that the ratio
of cost to weight is the same
for all melons, then we can
write this proportion.
|
 |
 |
| We let x represent the cost
(in dollars) of the big melon
and we substitute the given
values. |
 |
 |
| To solve this equation for x,
we can multiply both sides
by 26.
|
 |
 |
| We simplify. |
5.2 |
= x |
The cost of the big melon is $5.20.
|
