Check every column before you start. Any of them might be short.
Step 1: Let's Learn
Read it, or press Listen and follow the words.
Break a unit open
If the ones are short, break a ten. If the tens are short, break a hundred.
Across a zero
If there are no tens to break, break a hundred first, then break one of the new tens.
Check by adding
Add your answer to what you took away. You should get back to the start.
Opening a unit, once more
When a column has too little to subtract from, open one unit from the column to its left: a hundred becomes ten tens, a ten becomes ten ones. The value of the number never changes — only how it is packaged. Everything about three-digit subtraction rests on this one move.
Counting up instead
For 503 - 486, subtracting in columns means opening across a zero, which is fiddly. Counting up is easier: from 486, add 4 to reach 490, then 10 to reach 500, then 3 to reach 503. That is 4 + 10 + 3 = 17. Same answer, no regrouping at all.
Choosing between the two
When the numbers are close together, count up. When they are far apart, subtract in columns. Recognising which situation you are in is a genuine part of being fluent, and it is why fluency is not the same as memorising one procedure.
Step 2: Try It Yourself
Tap and try it out.
Start with
Taken away
What is left
Hundreds
3
Tens
5
Ones
5
502 − 147 = 355
Take 147 away from 502. The faded blocks are the ones that left.
Step 3: Watch an Example
One step at a time.
Watch Ana Cross a Zero
Ana works out 502 − 147.
- Step 1
She checks the ones: 2, and 7 have to go. Not enough.
Step 4: Your Turn
Practice makes it stick.
The Collection
Problem 1 of 2
A collection of 613 stamps loses 248. How many are left?
stamps
The Target
Problem 2 of 2
A target of 800 has 342 done. How many are left?
left
Subtract Within 1,000
1 of 4
624 − 358 = ?
2 of 4
700 − 265 = ?
3 of 4
486 − 253 = ?
4 of 4
Check it: 233 + 253 = ?
Step 5: Quick Check
Show what you know.
Question 1 of 2
905 − 348 = ?
Question 2 of 2
How do you check a subtraction?
What You Learned
- Check every column before you start.
- Break a hundred or a ten when a column runs short.
- Check the answer by adding it back.