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?
Interactive popup. Assistance may be required. The man has 12 boxes of batteries . Each box contains four batteries.
What is the problem asking?
Interactive popup. Assistance may be required. How many batteries does he have?
What mathematical operation should you use?
Interactive popup. Assistance may be required. Multiplication
How did you know which operation to use?
Interactive popup. Assistance may be required. The problem is asking to add the same number several times.
Write an equation that you could use to solve for the total number of batteries.
Interactive popup. Assistance may be required. T = 12 • 4
How many batteries does he have?
Interactive popup. Assistance may be required. 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?
Interactive popup. Assistance may be required. The discount is 20% and the original price is $1500.
What is the problem asking?
Interactive popup. Assistance may be required. What is the amount of the discount in dollars?
Which mathematical operation should you use?
Interactive popup. Assistance may be required. Multiplication
How did you know which operation to use?
Interactive popup. Assistance may be required. 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.
Interactive popup. Assistance may be required. D = 0.20 • 1500
What is the amount of the discount?
Interactive popup. Assistance may be required. 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.