Lesson 3 — Activity 1: Adding and Subtracting Whole Numbers
Completion requirements
Lesson 3 — Activity 1: Adding and Subtracting Whole Numbers
Getting Ready
Adding and subtracting numbers and quantities are important skills used in many everyday situations.
Think about This:
Think about the many different times you have used addition and subtraction at home, while out in your community, or in the workplace in the last week.
This activity will review addition and subtraction of whole numbers. You can use many strategies to add and subtract numbers: mind math, drawings, manipulatives, paper and pencil, or a calculator.
Digging Deeper
Whichever strategy you use, it is important to understand the process of addition and subtraction.
Click here for information on the processes of adding and subtracting.
Information courtesy of K&E Studio
Digging Deeper
Whichever strategy you use, it is important to understand the process of addition and subtraction.
Click here for information on the processes of adding and subtracting.
Information courtesy of K&E Studio
Click on the links below to find further information on addition and subtraction processes:
Remember that addition and subtraction are related operations.
496 + 241 = 737 241 + 496 = 737 Subtraction sentences can be written two ways:
737 – 496 = 241 737 – 241 = 496 Together, these four mathematical sentences make a fact family.
241 + 496 = 737 737 – 496 = 241 737 – 241 = 496 |
Click here to find extra practice questions on addition.
Click here to find extra practice questions on subtraction. Answers are supplied!
Estimating Sums and Differences
When you are solving addition or subtraction problems, you do not always need to find the exact answer. Sometimes, a close approximation or estimate will give you enough information to solve the problem.
When estimating, numbers are rounded to make calculations easier to work with.
Try This:
You may remember this problem from the Lesson 1 assignment:
Tommas has two savings accounts. In the first one, he has $324
and in the second he has $896. He also has $245 in a chequing account.
Use rounding to 100 to estimate the amount of money Tommas has in each account.
When you have done this, add your estimates together to see how much he has approximately in all three accounts.
$324 rounds to $300
$896 rounds to $900
$245 rounds to $200
$300 + $900 + $200 = $1,400
Tommas has approximately $1,400 in all three accounts.
He actually has $1,465, so the estimate is very close.
Let's try estimating with a subtraction problem.
A cookie factory can make 9,200 cookies each day. By midday, 6,734 cookies were mixed and baked. About how many cookies would be made in the afternoon?
9,200 – 6,732 =
Round to the nearest thousand:
9,000 – 7,000 = 2,000
Approximately 2,000 cookies would be made in the afternoon.
The actual number if cookies made in the afternoon is 2,468, so the estimate was quite close.
Estimates become less accurate as you round greater place values (e.g., tens, hundreds, one thousands).
AND
Estimates become more accurate as you round to lesser place values (e.g., ones, tenths, hundredths).
You will have further opportunities to estimate to lesser place values in later lessons.
Estimating by Front End
Estimation
Here is another way you can estimate. Front end estimation most of the time produces a closer estimate of sums or differences than the answer produced by adding or subtracting rounded numbers.
With Adding:
-
Add the digits of the two highest place values.
- Insert zeros for the other place values.
4,496 + 3,745
becomes
4,400 + 3,700 = 8,100
The actual answer to this equation is 8,241, so the estimate is quite close.
With Subtracting:
You can do front end estimation with subtraction as well.
-
Subtract the digits of the two highest place values
- Insert zeros for the other place values
7,396 - 3,745
becomes
7,300 - 3,700 = 3,600
The actual answer to this equation is 3,651, so the estimate is very close.
Go to the next page to try a Self-check Activity on adding and subtracting whole numbers.