Pre-Algebra Demystified

EXAMPLE

If 8 oranges cost $2.00, find the ratio of oranges to cost.

SOLUTION

8 oranges

2 dollars

¼

4 oranges

1 dollar

¼

4 oranges

$ 1 : 00

PRACTICE

1. Find the ratio of 10 to 25.


2. Find the ratio of 9 to 5.


3. Find the ratio of 80 miles to 2 hours.


4. Find the ratio of 2 yards to 60 cents.


5. Find the ratio of one nickel to one quarter.

ANSWERS

1.

2

5

2.

9

5

3.

40 miles

1 hour

4.

1 yard

30 cents

5.

1

5

Proportion

Aproportionis a statement of equality of two ratios. For example,^34 ¼^68 is a

proportion. Proportions can also be expressed using a colon, as 3 : 4¼6:8.

A proportion consists of 4 terms. Usually it is necessary to find the value of

one term given the other three terms. For example,^58 ¼ 24 x. In order to do this,

it is necessary to use a basic rule of proportions:

a

b

¼

c

d

if ad¼bc

In other words,^34 ¼^68 if 3 8 ¼ 4 6or24¼24. This is calledcross

multiplication.

154 CHAPTER 8 Ratio and Proportion