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## Multi-digit multiplication

Current time:0:00Total duration:2:15

# Multiplying 3-digit by 1-digit (regrouping)

CCSS Math: 4.NBT.B.5

## 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.