Lesson 1 — Activity 3: When to Use an Operation



Getting Ready


You will come across many instances in your home and work life where you will need to decide what math operation is best to use. For example, you may be having a BBQ and need to figure out how many burgers to buy at the grocery store based on the number of people you invited. What would be the best math operation to use to figure this out — would it be addition, subtraction, multiplication, or division?


Try This:

Let's take a closer look at the BBQ example. Say you are throwing a backyard party and want to invite 10 of your closest friends. You want to have enough food, so you plan to have two burgers for each of your guests. So, how many burgers will you need to buy?



    The best operation to use in this case would be either addition or multiplication.

    You could do either of the following calculations to figure out how many burgers to buy:


    Addition:

    10 + 10 = 20 burgers

    Multiplication:

    10 x 2 = 20 burgers


Let's look at a couple more examples.

While working in a store, you may need to help your boss with some basic math calculations. For example, if she asks you to set out 20 bottles of glue on four shelves, you will have to decide how many bottles can go on each shelf. You need to decide on what math operation your can use to figure out how many bottles go on each shelf.

Courtesy of Microsoft Office/Trevor Durstling

Courtesy of Microsoft Office/Trevor Durstling

How would you divide the bottles of glue evenly onto the shelves? In this case, you are putting the bottles into groups, so you can use the division sign on your calculator to divide the bottles into four groups to find out how many to put on each shelf.

Use your calculator to enter the following (note that your calculator might have either sign for division):

20 / 4 = 5

OR

20 ÷ 4 = 5


Another way to figure this out is to add as follows:

4 + 4 + 4 + 4 + 4 = 20

So you can put five bottles on each shelf.

A customer has come into the store and wants to buy towels. She tells you that she only has $50. You find the towel section and see that the towels are $10 each.

How would you answer this customer's question: "How many towels can I buy for $50 if the towels are $10 each?"

You need to decide which math operation to use. Will you add, subtract, multiply, or divide?





Courtesy of Microsoft Office/Trevor Durstling

For example, you could add:

1 towel at $10 + 1 towel at $10 + 1 towel at $10 ... until you reach $50.

10 + 10 + 10+ 10 + 10 = 50

That makes a total of five towels.

Or you could divide:

50/10 = 5

50 ÷ 10 = 5

50 dollars = five towels at $10 dollars a piece.

When trying to decide on which math operation you will use, think about what the problem is asking of you. Look at the table below, which will help you figure out which operation to use based on keywords.


Courtesy of ADLC

It will also help if you follow these steps:

Step 1: Understand the problem

  • Read the problem carefully.

Step 2: Make a plan

  • Identify a strategy to use and estimate your answer.


Step 3: Carry out the plan

  • Use the strategy you chose, and reach a solution.


Step 4: Look back

  • Is your answer reasonable?
  • Is your math accurate?


Courtesy of ADLC

Working in a store!

Try answering these 4 job task scenario questions 


  Self-check!

Try this!

You are working at Jim's Cafe and have been assigned some duties.

You have 100 Newspapers delivered every day. At the end of the day today you have 12 that have not sold. How many were sold during the day?

How would figure this one out? What operation did you use?

If you begin with 100 newspapers and end the day with 12 you can use subtraction to find out how many were sold. You can use your calculator to subtract the 12 that are left over from the 100 we began with.

100 - 12 = 88

That means we sold 88 newspapers during the day.

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