Positive and Negative Integers
Primary 4 · Mathematics
Positive and Negative Integers
Lesson 4 of 4
30 min
Let's begin
Early one morning in Kinigi the temperature is −3 °C. By lunchtime it is 4 °C. Niyonzima wants to know: by how many degrees did it warm up? He counts on the number line.
The distance between two integers is the number of steps from one to the other on the number line. A distance is never negative: it is just how far apart the numbers are.
From −3 up to 0 is 3 steps. From 0 up to 4 is 4 more steps. So the distance is 3 + 4 = 7. The temperature rose by 7 degrees.
The lift. A lift goes from the car park, floor −2, up to floor 5. It passes 2 floors to reach the ground floor and 5 more to reach floor 5: 2 + 5 = 7 floors.
The debt. Habimana owes his friend 300 Frw (−300). He is paid 1 000 Frw for helping at the market and pays the debt. He now has 1 000 − 300 = 700 Frw. From −300 to 700 is 300 + 700 = 1 000 steps, which is exactly the 1 000 Frw he earned.
Explore: the Number Line: Distance simulation lets you move a person and a house, a fish and a bird, or two temperatures along a number line and shows the distance between them.
Tip
Opposite sides? Add. Same side? Subtract. Look at where zero is first, then decide.
Work each one in your exercise book first. Then tap Show answer to check.
What is the distance between 0 and −9?
Answer: 9
What is the distance between −5 and 3?
Answer: 8 (opposite sides: 5 + 3)
What is the distance between −8 and −1?
Answer: 7 (same side: 8 − 1)
In the morning it is −6 °C. In the afternoon it is 9 °C. By how many degrees did the temperature rise?
Answer: 15 degrees (6 + 9)
A lift goes down from floor 4 to floor −3. How many floors does it go down?
Answer: 7 floors (4 + 3)
What you learned today
Sources and credits
The stories, Rwandan worked examples, diagrams and practice questions were written by Ganzaa.
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