For 425 − 172 there are only 2 tens, and 7 tens need to go.
Step 1: Let's Learn
Read it, or press Listen and follow the words.
Open a hundred
Break one flat into ten rods. Now there are 3 hundreds and 12 tens.
It is still 425
3 hundreds, 12 tens and 5 ones is 425. Nothing was added or lost.
This is the same move as breaking a ten, just one place further left.
Not enough tens
In 425 - 173 the tens column asks for 7 tens from only 2 tens. There are not enough, so open a hundred. One hundred becomes ten tens, and 425 is rewritten as 3 hundreds, 12 tens and 5 ones. Same value, different packaging.
A worked case: 425 - 173
After opening a hundred: ones, 5 - 3 = 2. Tens, 12 - 7 = 5. Hundreds, 3 - 1 = 2. Answer: 252. Check by adding: 252 + 173 = 425. Correct.
Record the change on the page
Cross out the 4 and write 3 above it; cross out the 2 and write 12. Doing this on paper rather than in your head is what keeps you from subtracting the hundreds with the old digit. Every experienced subtractor writes this down.
Step 2: Try It Yourself
Break a hundred open and watch the tens column grow.
Start with
Taken away
What is left
Hundreds
2
Tens
5
Ones
3
425 − 172 = 253
Take 172 away from 425. The faded blocks are the ones that left.
Step 3: Watch an Example
One step at a time.
Watch Ana Open a Hundred
Ana needs to take 172 from 425.
- Step 1
She checks the tens: only 2, and 7 have to go.
Step 4: Your Turn
Practice makes it stick.
Another Way to Show It
Problem 1 of 2
2 hundreds, 15 tens and 4 ones is which number?
The Shop
Problem 2 of 2
A shop had 634 items and sold 281. How many are left?
items
Open a Hundred
1 of 4
526 − 183 = ?
2 of 4
748 − 265 = ?
3 of 4
3 hundreds and 14 tens is which number?
4 of 4
859 − 327 = ?
Step 5: Quick Check
Show what you know.
Question 1 of 2
635 − 172 = ?
Question 2 of 2
Breaking a hundred gives you how many tens?
What You Learned
- If there are not enough tens, break a hundred open.
- One hundred becomes ten tens.
- The amount stays exactly the same.