You can add or multiply two numbers in either order: 4 × 7 = 7 × 4 (a turnaround). When multiplying three numbers, you can also choose which two to multiply first. Look for a friendly pair that makes 10 or 100, such as 2 × 5 or 4 × 25. You can also split a factor to make a friendly pair: 16 × 25 = 4 × 4 × 25 = 4 × 100.
Explore this idea with maths tools
Maths you can move
Build 8 + 5
Tap two gold counters to fill the ten-frame.
8 in the frame + 5 waiting. The total stays the same.
Words to know
- turnaround fact
- the same two numbers in the other order give the same answer
- friendly pair
- two factors that make 10, 100 or another easy number
Worked examples
4 × 7 = 7 × ?
- 1.A turnaround uses the same two numbers.
- 2.4 × 7 = 7 × 4.
= 4
4 × 9 × 25 = ?
- 1.Put the friendly pair together: 4 × 25 = 100.
- 2.100 × 9 = 900.
= 900
16 × 25 = 4 × ?
- 1.Split 16 into 4 × 4: 16 × 25 = 4 × 4 × 25.
- 2.Group the last two: 4 × 25 = 100, so 16 × 25 = 4 × 100.
= 100
For parents
Method: Change the order, change the grouping
What to say: Can you change the order to make it easier? Which two numbers make 10 or 100?
Common mistakes:
- Copies the number already next to the box instead of finding the one that makes both sides equal.
- Reads the equals sign as 'the answer comes next' and writes the value of the left side.
- Multiplies the friendly pair and forgets the third factor.
- Multiplies the friendly pair and then adds the third factor instead of multiplying by it.
- Writes one zero too many when multiplying by 10 or 100.
- When one factor gets smaller, makes the other factor smaller too instead of bigger.
- Keeps the sum of the numbers the same instead of the product (additive compensation).