Multiplication is an operation that has several applications in mathematics:

 You can use multiplication to represent repeated addition when you combine several groups that each have the same number of items. I have 5 bags of candy; each one has 7 pieces in it. How much candy do I have? 5 • 7 = 35 pieces of candy You can multiply something by a scale factor to make it larger or smaller. Mark usually leaves a tip that is equal to 20% of the total bill at a restaurant. If the bill came to \$12.00, how much will he leave as a tip? 0.20 • 12 = \$2.40 You can multiply a rate times time to get a total amount of something. I drove 45 miles per hour for 3.5 hours. How far did I travel? 45 • 3.5 = 157.5 miles You can use it to find areas of some geometric shapes. A rectangle has a length of 2 feet and a width of 0.4 feet. What is the area of the rectangle? 2 • 0.4 = 0.8 square feet

Read the following examples, and answer the questions below using your notes. After some of the questions, you will see the word "Hint:" Hover your cursor over the word "Hint" if you need help answering that question.

Example 1:

In this problem you were given a rate and a time and then asked for a total amount. This requires multiplying rate times time.

Example 2:

A man has 12 boxes of batteries. If each box has four batteries in it, how many batteries are there in all?

What information are you given in the problem?

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The man has 12 boxes of batteries . Each box contains four batteries.

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How many batteries does he have?

What mathematical operation should you use?

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Multiplication

How did you know which operation to use?

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Write an equation that you could use to solve for the total number of batteries.

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T = 12 • 4

How many batteries does he have?

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T = 48. The man has 48 batteries.

In this problem you were asked to add together several groups of the same amount. Multiplication is repeated addition.

Example 3:
A music store is offering a sale of 20% off all pianos. How much would you save on a piano if the original cost was \$1500?

What information are you given in the problem?

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The discount is 20% and the original price is \$1500.

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What is the amount of the discount in dollars?

Which mathematical operation should you use?

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Multiplication

How did you know which operation to use?

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This problem is asking for a portion of something larger. You find this by multiplying the amount by a percent (or fraction).

Write an equation that you could use to solve for amount of the discount.

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D = 0.20 • 1500

What is the amount of the discount?

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D = 300. The discount is \$300.

This problem used multiplication by a scale factor. This time, a percent was used to find a part of a larger whole.

Based on these three sample problems, brainstorm a list of clues that you could find in a word problem that would let you know that you should use multiplication. Record these using your notes.