Lesson 1 — Activity 1: Estimation with Whole Numbers




Getting Ready


Using estimation is a skill for life. For example, below are some things that you could use estimation for in your daily life:

  • how much a bill will be
  • which item is the best value for your money
  • the size, area, or angles of things

It might also be helpful if you could quickly guess how many people are in a room, how many cars are on the street, or how many boxes are on a shelf.

We do not always need to find the exact answer to a problem. Sometimes a close approximation, or estimate, gives us enough information to make decisions.

When we use estimation, we are not talking about exact answers but, instead, answers that are close enough to the right answer!

Try This:

You want to buy five magazines that cost $1.95 each. When you go to buy them, the cost is $12.25. Use estimation to see if that amount sounds right.


Five magazines at $1.95 each is about 5 times $2, or about $10, therefore, $12.25 seems too much! If you were to double check the exact price by adding $1.95 five times, the total would be $9.75, which is closer to your estimate of $10. Therefore, you are being charged too much if the clerk asks for $12.25.


Let's take a look at an example!

In the example below, you will begin by rounding the dollar amounts (without the cents) to the nearest $5 for the three items: a belt, a shirt, and jeans. Then you will be given the actual amount of the three items.



Courtesy of Learn Alberta





Courtesy of ADLC

When estimating, numbers are rounded to make calculations easier to work with.

Estimating the cost of food items can save you time when shopping. For example, if you were buying snacks for a party, you may be looking at buying the following items:

  • a case of pop
  • a box of chocolate bars
  • a box of chips


Estimating is just rounding up or down to the nearest place value.

Remember!


  • Any number that is 5 or higher than 5 is rounded up.

  • Any number that is below 5 is rounded down.

For example:

$19 has a 9 in the ones place, which is higher than the number 5, so we round it up to $20.

$13 has a 3 in the ones place, which is lower than the number 5, so we round it down to $10.

$15 has a 5 in the ones place, which is the middle, so we round it up to $20.


Let's take another look at the shopping example above.

Click here to see an example of estimating the cost of shopping to buy the snacks for your party.

Click here to try an interactive activity rounding up or down using a simple number line.


Click here to play a game where you will practise your rounding and estimation skills. Click on the "Instructions" button to begin. After you have read the instructions, click on the "Play Game" button. Have fun!


  Self-check!

Try this!


Practice estimating and rounding different food costs. Answer these questions on your own first. When you are finished, click on the tabs below to check your answers!


In your mind estimate the costs of...$4 a bag of popcorn.


In your mind estimate the costs of...$9 a box of corn chips.


Estimate the costs of $4 and $9.


If you said $15 you are right!

What is the actual cost of $4 and $9?


If you said $13 you are right!


Digging Deeper


Click on the Play button below to watch a video to review how to round larger numbers.