hey there my name is kayleigh and this lesson is about multiplying big numbers
three-digit numbers by three digit numbers and four digit numbers by four
digit numbers are you ready let's get started
so you'll see here I have two three-digit numbers that I'm multiplying
so the first thing I'm going to do is I'm gonna take this horizontal
expression here I'm going to write it vertically so I have 722 times
118 equal so just like when I multiply two-digit numbers together I'm gonna
start with my ones column on the bottom and I'm going to multiply my ones column
by each column in the top number so eight times 216 I carry that one 8 times
2 is 16 I add that one 17 8 times 7 56 plus I add that one I get a 57 now I
need to multiply my tens column on the bottom but the first thing I do is I add
a 0 in that ones place here 1 times 2 - 1 times 2 - 1 times 7 7 now I'm going to
multiply my hundreds place on the bottom number so I need to go one two zeros in
the bottom place 1 times 2 - 1 times 2 - 1 times 7 7 now I just add all of these
here 6 + 0 6 7 + 2 9 7 + 2 9 plus another 2 11 I carry that one so now I
have 7 8 9 10 plus 5 I know is 15 carry that one now 7 plus 1 is 8 and there is
my final number that's a 6 there now let's see which one of these matches
looks like this one here so there we have our answer nice job so we're gonna
take it up a notch now and multiply to four digits numbers together so first
things first I'm going to write this as a vertical expression multiplied by 2398
so same idea I'm going to start with my ones calm and we'll work my way across
the bottom number multiplying by each column and my top number so 8 times 8 64
I got a 4 down here I carry my six 8 times 0 is 0 but I have that 6 that I
add to it 8 times 2 16 I carry that one 8 times 2 is 16 I add that one 17 so now
I'm going to my tens place on the bottom number and adding a zero to that ones
place 9 times 8 is 72 I put a 2 here now that 6 turns into a 7 so 9 times 0 is 0
but I have a 7 up there that I add 9 times 2 18 carrying that one 9 times 2
is 18 plus that one is 19 moving to my hundredths column now so I add 0 in the
ones and the 0 in the tens 3 times 8 is 24 I put a 4 down there so now I have a
2 up here 3 times 0 is 0 but I have that too
3 times 2 is 6 and 3 times 2 again is also 6 great now I'm moving to my
thousands place in the bottom number so I put a 0 in the ones as 0 in the tens
and a zero in the hundredths place two times 8 16 now I have a 1 up here 2
times 0 is 0 but I have that 1 2 times 2 is 4 and 2 times 2 is 4 already so now I
got to add all these numbers up together I get a 4 in my ones place 6 plus 2 I
get an 8 6 plus 4 is 10 plus 7 I get a 17 carrying my 1 I get eight nine 10
sixteen seventeen plus 8 9 10 16 17 plus 7 so 17 18 19 20 21 22 23 24 carry my 2
you up here I get 9 10 11 12 13 plus 6 gives me in 19 Terry my 1 at 1 2 plus 6
is 8 8 plus 4 gives me 12 carry my 1 4 plus 1 is 5 and there is my final answer
I'll box that up make sure it has a match over here and it does it's a great
job now we've done three digit and four digit numbers and I hope that you saw
the pattern there we work our way across our bottom numbers starting with the
ones column we multiply all the way across our top number then as we move on
we add a 0 in every place value that we've moved from so when I'm going to my
tenths place I put a 0 in my ones place answer and then you saw as we got all
the way over here to the thousands place we added zeros to our ones tens and
hundreds columns so you just got to make sure you keep track of all of those
carrying numbers that we did but great job so keep practicing this by doing the
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