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### Course: Arithmetic (all content)>Unit 2

Lesson 17: Subtraction with regrouping within 1000

# Worked example: Subtracting 3-digit numbers (regrouping twice)

Sal using regrouping (borrowing) to subtract 913-286. Created by Sal Khan.

## Want to join the conversation?

• Can you regroup in subtraction?
• Yes, you can regroup in subtraction but it is more commonly called BORROWING instead of regrouping. If you are taking 68 away from 243, you would need to regroup, because you wouldn't be able to take 8 ones away from 3 ones, so you would have to regroup or BORROW from the tens column. You would also need to regroup because you wouldn't be able to take 6 tens away from 3 tens (since we just borrowed one of the tens), so we would need to borrow from the hundreds.
243=2 hundreds, 4 tens, 3 ones but it also equals 2 hundreds, 3 tens, 13 ones
now we can take the 8 ones in 68 away from the 13 ones in 243, which leaves us with 5 ones
So now we have 243=2 hundreds, 3 tens, 13 ones but it also equals 1 hundred, 13 tens, 13 ones
now we can take the 6 tens in 68 away from the 13 tens in 243, which leaves us with 7 tens
we can also take away the 0 hundreds in 68 from the 1 hundred in 243, which leaves us with 1 hundred
• What are some tricks/methods I can learn in order to solve this problem (and other 3-digit problems) mentally? I can solve addition and subtraction problems mentally if they are one or two-digit numbers but whenever it's a 3-digit I get stumped because I lose track of the numbers I'm regrouping. Thank you.
• If you're having trouble with this, try using a piece of paper for help. I'm in middle school, and even now i sometimes have to do addition and subtraction on paper. There's no shame in using a piece of paper or showing your work
• is the expanded form different the original way?
• you're just adding zeros. the expanded form is just a bit easier. Like if you don't exactly get the number. say, 7,483,655. in expanded form it would be 7,000,000+400,000+80,000+3,000+600+50+5
• i dont understand subtraction why cnat we subtract 300-500?
ans: yes we can we get a negative number -200
im confused?because people say you cannot subtract a small number by big number?
• You can subtract a smaller number from a larger number. Younger level teachers don't want to confuse their children, so they say that you can't do this. In higher math, teachers say you that you can.

I hope this helps!
• Why does Sal have 100 in the tens place and 13 in the ones place?
• You always subtract by starting from the right most digits.
3-6 doesn't work, so you borrow a 10 from the tens place, making 13 ones leaving 0 tens.
Looking ahead, you realize that you can't take 8 from 0, so you borrow from the hundreds, putting 10 in the tens and leaving 8 in the hundreds.
He expanded each place, making the 10 tens a hundred.
• How is 900-800=200,it should be 100
• I know that 900 - 800 isn't 200, the answer is 100, but he didn't say that. it's fine though, because everybody makes mistakes.
(1 vote)
• i cant do it
(1 vote)
• Ok here is a bunny🐇
• how can he take that from the tens