A number can be split into parts in many ways. 46 is 40 + 6, but if you break one ten into ones it is also 30 + 16. Nothing is lost: the parts still add to 46. In the same way 352 = 200 + 150 + 2, and because every hundred is 10 tens, 352 is 35 tens and 2 ones. Check by adding the parts back together.
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
- partition
- split a number into parts that add back to it
- regroup
- change a ten into ten ones, or a hundred into ten tens
Worked examples
46 = 30 + ?
- 1.46 is 4 tens and 6 ones. 30 uses only 3 tens.
- 2.1 ten and 6 ones are left: 16.
= 16
352 = 200 + ? + 2
- 1.200 is one hundred fewer than 300, so that hundred joins the 5 tens.
- 2.10 tens + 5 tens = 15 tens = 150.
= 150
352 = ? tens and 2 ones
- 1.3 hundreds are 30 tens.
- 2.30 tens + 5 tens = 35 tens.
= 35
For parents
Method: Break a ten (or a hundred) into smaller parts
What to say: What happens if we break one of the tens? Do the parts still make the whole number?
Common mistakes:
- Gives the digit's usual part (the ones digit, the tens part or the tens digit) without regrouping.
- Regroups the larger place but forgets the digits in the smaller place.
- Reads '=' as 'work out the answer' and adds the numbers shown.
- Takes away only the first part shown and forgets the other.
- Gives the value of the tens (350) instead of how many tens there are (35).