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# Multiplying 4-digit by 1-digit (regrouping)

Learn to multiply a 4-digit number by a 1-digit number.  In this video, we will multiply 8085 times 9. Created by Sal Khan.

## Want to join the conversation?

• can u do the same thing or concept for billion
• Yes you can. The possibility of multiplying different numbers is infinite.
• why are there negitive numbers?
• You can imagine that negative numbers mean something owed. It's not that you can hold negative something, but rather you need to take that number from something else. For example I have 25 apples and you want 5. So 25-5 = 25 + (-5) represents you taking the 5 from me.
• I'm surprised no one uses this for chat
• you don't need to use this for chat because u probably don't even know anybody here and it's no fun
(1 vote)
• if you change the places will you need to do more work then you orignaly did (im bad at spelling sorry)
• Yep! It's ok that you aren't good at spelling as long as others can understand you, and I can.
• so 5x2 is like 2+2+2+2+2 so 5x2=10 so 2+2+2+2+2 ok i can do that?
• Yes. That is a common strategy for multiplication.
(1 vote)
• i need to learn my fact in my head
• That's what i do but it gets diffucult in your head and it messes up the problem
• Do you sometimes need to divide when you're regrouping,or is it just plain multiplying?
• the multi digit multiplication is so easy and now i under stand it better than before.
• what is 90,99999999x5000,999999=
what.