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External Video

Ratio

	In a class there are two girls for every three boys. The ratio 2 : 3 compares the number of girls to the number of boys. 2 and 3 are called terms in the ratio where 2 is the first term and 3 is the second term. This can also be represented as . We can write the ratio of girls to the whole class as 2 : 5.

• What is the ratio of boys to the whole class?

  Answer

• If this class has eight girls, determine how many boys there are using the ratio that there are two girls for every three boys.

  Answer

Proportions and Common Multipliers

In this exploration you will be given proportions with unknown values. Model each proportion with counters and use the model to find the unknown value, or answer.

1. Download Student Exploration: Proportions and Common Multipliers Exploration.
2. Read the Overview on page 1 which contains instructions for using the Gizmo.

• It is important to click the Group counters icon before you click the Check model icon.
• Pay attention to how the counters are arranged in groups.

3. Work through the Activity questions on pages 2 and 3 of Student Exploration: Proportions and Common Multipliers Exploration.
4. Launch the Proportions and Common Multipliers Gizmo.
5. Answer the five assessment questions located below the Gizmo. Check your answers when you finish.

Ratios and Proportions

Go to the Math Is Fun website to learn more about ratios. Review the information you find there.

Practice Exercise

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