Multiplication and Division of Integers
Primary 6 · Mathematics
Multiplication and Division of Integers
Lesson 1 of 5
25 min
Let's begin
On a cold night near the top of Mount Karisimbi, the temperature can fall below 0 °C. A climber writes “−3 °C” in her notebook. Down in Kigali, a lift in a tall building has buttons for floors 3, 2, 1, 0 … and also −1 and −2 for the car park under the ground.
Numbers below zero are all around us. In this unit you will learn to multiply and divide them.
Integers are the whole numbers, their opposites and zero: … −4, −3, −2, −1, 0, +1, +2, +3, +4 …
| Situation | Positive | Negative |
|---|---|---|
| Temperature | 18 °C in Kigali in the morning: +18 | 3 degrees below zero: −3 |
| Mobile money | You receive 2 000 Frw: +2 000 | You owe 500 Frw: −500 |
| Height and depth | A hill 200 m above the lake: +200 | A diver 30 m under the surface of Lake Kivu: −30 |
| Football | Scored 3 more goals than you let in: +3 | Let in 2 more goals than you scored: −2 |
Negative integers sit to the left of zero and positive integers to the right. Two numbers that are the same distance from 0 but on opposite sides are opposites: 4 and −4 are opposites.
The further right a number is, the bigger it is. So −2 > −5, because −2 is to the right of −5. (Think about temperature: −2 °C is warmer than −5 °C.)
Adding a positive number moves you right; adding a negative number moves you left. The picture shows ( − 2) + ( − 3): two steps left, then three more steps left, landing on −5.
Hold on to this idea. Multiplication is repeated addition, so in the next lesson 3 × ( − 2) will simply mean ( − 2) + ( − 2) + ( − 2).
Explore: open the Number Line: Integers simulation. Drag points onto the line, compare them, and try the bank-account and elevation scenes.
Tip
Left is less. On the number line, the number on the left is always the smaller one, even when both numbers are negative. −10 °C is colder than −1 °C.
Work each one in your exercise book first, then tap Show answer to check.
Write an integer for: a lift goes down to the second floor under the ground.
Answer: −2
Write the opposite of −15.
Answer: 15 (or +15). It is the same distance from 0 on the other side.
Which is bigger, −8 or −3?
Answer: −3, because it is further to the right on the number line.
Work out ( − 4) + ( − 5).
Answer: −9. Move 4 left, then 5 more left.
Arrange from smallest to biggest: 3, −6, 0, −1, −9.
Answer: −9, −6, −1, 0, 3.
What you learned today
Sources and credits
The stories, Rwandan worked examples and practice questions were written by Ganzaa.
Quick check
Umutoni owes 300 Frw on her mobile money account. Which integer shows this?
