Positive and Negative Integers
Primary 4 · Mathematics
Positive and Negative Integers
Lesson 2 of 4
25 min
Let's begin
Ishimwe stands at the ground floor of a tall building. He goes up 4 floors to visit his aunt. His friend Byiringiro goes down 4 floors to the car park. They both travelled 4 floors, but in opposite directions. The number line helps us to picture this.
Zero sits in the middle. Positive integers go to the right of 0, and negative integers go to the left. The steps between the marks are all the same size.
To place −4, start at 0 and take 4 steps to the left. To place 4, take 4 steps to the right.
Two numbers are opposites when they are the same distance from 0 but on different sides. 4 and −4 are opposites. So are 25 and −25.
The opposite of 0 is 0.
Go 4 steps right, then 4 steps left, and you are back at 0: 4 + ( − 4) = 0. Because of this, the opposite of a number is also called its additive inverse. Adding it "undoes" the number.
Ishimwe goes up 4 floors and then down 4 floors: he is back on the ground floor, 0.
Explore: open the Number Line: Integers simulation. Drag points onto the line, show their opposites, and try the elevation and bank-account scenes.
Tip
Mirror at zero. Imagine a mirror standing at 0. A number's opposite is its reflection: same distance, other side.
Work each one in your exercise book first. Then tap Show answer to check.
Start at 0 and take 6 steps to the left. Where are you?
Answer: −6
What is the opposite of −15?
Answer: 15
What is the opposite of 0?
Answer: 0
Work out 9 + ( − 9).
Answer: 0. A number plus its opposite is always 0.
Name all the integers between −3 and 2.
Answer: −2, −1, 0 and 1
What you learned today
Sources and credits
The stories, Rwandan worked examples, diagrams and practice questions were written by Ganzaa.
Quick check
What is the opposite of −12?
