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### Course: 4th grade > Unit 3

Lesson 5: Multiply with partial products# Multiplying 3-digit by 1-digit (regrouping)

Learn to multiply a 3-digit number by a 1-digit number using regrouping. In this video, we will multiply 7x253. Created by Sal Khan.

## Want to join the conversation?

- Has anyone ever wondered 4 digit by 4 digit(20 votes)
- why is this so hard?// maybe just me or bc its a monday.(10 votes)
- he said at0:42'carry appropriately' can you carry inappropriately(8 votes)
- how do you solve it with 10 digits?//(5 votes)
- What do you mean by 10 digits? Multiple 10 digits with 10 digits?(4 votes)

- did anyone else notice that he said one thousand seven hundred AND seventy one? The proper grammar is one thousand seven hundred seventy one.(4 votes)
- yeah i noticed that as well i'm kinda surprised he made that mistake since hes the one teaching us grammar(4 votes)

- How do you get better at memorizing multiplication facts?(1 vote)
- Practice is the only thing I can tell you :) There's no easy way to do it. Maybe try playing a math game online, there's tons of them for free. Sushi Monster is a good free app that helps you learn multiplication and division fast.(5 votes)

- If the question is easy enough (2 X 68 = ?) then i would just do it that way and times the two with the six then put awenswer in the thingy thing then i would times the eight and boom thats done... yes i am 11 and i know my puncuation is bad... and spelling.....(3 votes)
- At0:46, why did Sal circle the numbers? I tried it and it was too messy. I could hardly see the numbers! And once your done explaining why he circled the numbers, can you PLEASE,PLEASE,PLEASE tell me how Sal did it so neatly?(3 votes)
- He uses a Digital Pen. And obviously he knows how to use it. ;-;(1 vote)

- why did people create decimals and who thought of an idea to use it for learning?(3 votes)
- It is not a variable obviously(3 votes)

## Video transcript

Let's multiply 7 times
253 and see what we get. So just like in the last
example, what I like to do is I like to rewrite the
largest number first. So that's 253. And then write the
smaller number below it and align the
place value, the 7. It only has a ones place, so
I'll put the 7 right over here below the ones place in 253. And then put the multiplication
symbol right over here. So you could read
this as 253 times 7, which we know is the same
thing as 7 times 253. And now we are ready to compute. And there are many
ways of doing this, but this one you could
call the standard way. So what I do is I
start with my 7. And I multiply it times
each of the numbers up here, and I carry appropriately. So first I start with 7 times 3. Well, 7 times 3 we know is 21. Let me write that down. 7 times 3 is equal to 21. You could do this
part in your head, but I just want to
make it clear where I'm getting these numbers from. What I would do in
the standard method is I would write the
1 into 21 down here, but then carry the
2 to the tens place. Now I want to figure
out what 7 times 5 is. We know from our multiplication
tables that 7 times 5 is equal to 35. Now, we can't just somehow
put the 35 down here. We still have to deal with
this 2 that we carried. So we compute 7 times 5 is 35,
but then we also add that 2. So it's 35 plus 2 is 37. Now, we write the 7 right
over here in the tens place and carry the 3. Now we need to compute
what 7 times 2 is. We know that 7 times 2 is 14
from our multiplication tables. We can't just put
a 14 down here. We have this 3 to add. So 7 times 2 is
14, plus 3 is 17. So now we can write
the 17 down here, because 2 is the last number
that we had to deal with. And so we have our answer. 7 times 253 is 1,771.