Vocabulary

the values of a proportion that are close to each other when written in ratio form using a colon.

Extremes

the values of a proportion that are farther apart from each other when written in ratio form using a colon.

Cross Product Property of Proportions

states that the cross products of two ratios will be equal if the two ratios form a proportion.

Guided Practice

Here is one for you to try on your own.

Each pencil sold at the school store costs the same price. Caryn paid $1.12 for 14 pencils at the school store. Arnob also bought pencils, but he paid $0.48 for the pencils he buys. Write a proportion to represent
, the number of pencils that Arnob bought.

Answer

When setting up a proportion, we must be sure to use consistent terms. One way to set up a proportion would be to write two equivalent ratios, each comparing the total price to the number of pencils.

We know that Caryn paid $1.12 for 14 pencils. So, one ratio could be this one.

We know that Arnob paid $0.48. The number of pencils he bought is unknown, so we can use
to represent that number.

Since these two ratios are equivalent, we can put them together to form a proportion.

The proportion above could be used to find
, the number of pencils Arnob bought.

If Jake joined the two in shopping for pencils and purchased some of the same pencils, he would also have a ratio that would be equivalent to these two ratios. The situation is the same. Everyone is purchasing pencils. The pencils cost the same amount. Therefore, we have equivalent proportions as we compare pencils purchased with pencil price.