Classifying Numbers by Their Properties
Primary 4 · Mathematics
Classifying Numbers by Their Properties
Lesson 4 of 5
25 min
Let's begin
For a school celebration, Keza helps to set out 25 chairs. Her teacher asks her to make a perfect square: the same number of rows as chairs in each row. Keza makes 5 rows of 5. Can she do the same with 24 chairs?
When you multiply a number by itself, the answer is a square number. Square numbers make perfect squares of dots:
| Number | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
|---|---|---|---|---|---|---|---|---|---|---|
| Multiply by itself | 1 × 1 | 2 × 2 | 3 × 3 | 4 × 4 | 5 × 5 | 6 × 6 | 7 × 7 | 8 × 8 | 9 × 9 | 10 × 10 |
| Square number | 1 | 4 | 9 | 16 | 25 | 36 | 49 | 64 | 81 | 100 |
We say "5 squared is 25". 24 is not a square number, because no whole number times itself makes 24 (4 × 4 = 16 and 5 × 5 = 25). So Keza cannot make a perfect square with 24 chairs.
Finding the square root is the opposite of squaring. The square root of 25 asks: "Which number, multiplied by itself, makes 25?" The answer is 5, because 5 × 5 = 25.
We use the sign √ for square root: √25 = 5, √49 = 7, √100 = 10.
To find a square root, look for the number in the bottom row of the table and read the number above it.
Tip
Square it, then un-square it. 6 squared is 36, so the square root of 36 is 6. Learn the ten square numbers up to 100 by heart and square roots become easy.
Work each one in your exercise book first. Then tap Show answer to check.
What is 7 squared?
Answer: 49, because 7 × 7 = 49.
Is 30 a square number?
Answer: No. 5 × 5 = 25 and 6 × 6 = 36, so no whole number times itself makes 30.
Find √36.
Answer: 6
Find √100.
Answer: 10
Mugisha arranges 64 chairs in a perfect square. How many chairs are in each row?
Answer: 8, because 8 × 8 = 64.
What you learned today
Sources and credits
The stories, Rwandan worked examples, diagrams and practice questions were written by Ganzaa.
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