Factors, multiples, and primes (grade 4) · lesson

Multiples

💡 The multiples of a number are what you say when you count by that number.

Multiples of 8 are 8, 16, 24, 32, 40, and so on. Each one is 8 more than the last.

To find the next multiple, add the number once more. To list the ones in a range, count by the number and keep only the ones inside it.

🧠 Let's work it out

What is the next multiple of 8 after 32?

What do you think comes next?

💡 Find every factor by finding every pair of numbers that multiply to make the number.

Start with 1 times the number. Then try 2, 3, 4, and so on.

Stop when the pairs start to repeat. Every number in a pair is a factor.

🧠 Let's work it out

Find the factors of 16.

What do you think comes next?

💡 A prime number has exactly two factors, 1 and itself, and a composite number has more.

11 can only be made as 1 × 11. So 11 is prime.

25 can be made as 5 × 5 too. It has more than two factors, so it is composite.

An odd number can still be composite. Try dividing by 3, 5, and 7.

🧠 Let's work it out

Is 39 prime?

What do you think comes next?

💡 To find the smallest number that is a multiple of two numbers, count by the bigger one and check the smaller one.

Count by the bigger number. For each one, ask if the smaller number goes into it evenly.

The first one that works is the smallest multiple of both.

🧠 Let's work it out

Find the smallest multiple of both 5 and 6.

What do you think comes next?