Multiples, factors and primes
I can find factor pairs and multiples, and tell whether a number is prime.
For grown-ups: this lesson in words
Years 4 to 6 · Maths
Multiples, factors and primes: I can find factor pairs and multiples, and tell whether a number is prime.
Here are 12 apples in 3 rows. Each row has 4 apples.
Count in 4s: 4, 8, 12.
3 × 4 = 12, so 3 and 4 are a factor pair of 12.
Factors are the numbers that multiply together to make another number.
Picture: An array of 3 rows of 4 apples. The rows are counted in 4s: 4, 8 and 12.
Swap the numbers. The same 12 apples are now in 4 rows of 3.
Count in 3s: 3, 6, 9, 12.
4 × 3 = 12. It is still 12.
3 × 4 = 12 and 4 × 3 = 12. A factor pair works both ways round.
Picture: An array of 4 rows of 3 apples. The rows are counted in 3s: 3, 6, 9 and 12.
Let's find every factor pair of 12, in order. Start at 1: 1 × 12 = 12.
Then 2: 2 × 6 = 12. Then 3: 3 × 4 = 12.
2 + 10 = 12, but 2 × 10 = 20. Factor pairs multiply, so 2 and 10 are not a factor pair of 12.
4 × 3 is the same pair as 3 × 4, so we stop. 12 has 3 factor pairs.
Picture: Sorting into 2 groups: Factor pairs of 12, Not factor pairs of 12. Factor pairs of 12: 1 and 12 (counter), 2 and 6 (counter), 3 and 4 (counter). Not factor pairs of 12: 2 and 10 (counter).
Your turn: Here are 2 rows of 5 counters. That is 10 counters. Which factor pair of 10 does this array show?
Picture: An array of 2 rows of 5 counters.
Choose one:
- 2 and 5
- 2 and 10
- 5 and 10
Answer
The answer: 2 and 5
2 × 5 = 10, so 2 and 5 are a factor pair of 10.
Picture: An array of 2 rows of 5 counters. The rows are counted in 5s: 5 and 10.