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2 Digit Addition with Regrouping - Carrying and Place Value for Kids - FreeSchool - YouTube
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You're watching FreeSchool!
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Hi everyone!
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Today we're going to talk about regrouping
in two digit addition.
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When we write numbers with two digits we have
to pay attention to WHERE the numbers are
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written, because how much they are worth changes
based on where they are.
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This is called place value.
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When we're adding two digit numbers we only
have two places to worry about, and those
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are the tens column and the ones column.
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So, to demonstrate, if we write the number
'32,' then the 3 goes in the tens column and
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the 2 goes in the ones column.
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Because the two is in the ones column it is
worth 2 one-unit blocks, but the 3 is in the
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tens column, which means that it is worth
3 block stacks of ten units each.
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That 3 is really worth 30.
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Now let's try adding something to our 32:
11.
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11 is the same as one one-unit block and one
ten-unit block stack.
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We're going to start by counting all of our
ones - because we always start with the ones
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column.
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So, we have one, two, three ones blocks, so
we put a 3 in the ones column.
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Next we count our tens: one, two, three, four.
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We have four tens, so we put a four in the
tens column.
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Okay.
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That means that 32 + 11 is 43.
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That was easy.
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But what happens if we want to add 29 instead
of 11?
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29 is the same as 9 one-unit blocks and 2
ten-block stacks.
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So, let's count all of our ones again.
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1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11.
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2 + 9 equals 11, but we can't write that in
our ones column!
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Our ones column is only for numbers less than
10.
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So we have to change ten of our ones into
a ten-block stack, something we call 'regrouping.'
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That means we only have one single block left.
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So in the ones column, we will write 1.
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But now we have to do something with that
ten-block stack.
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Where do tens go?
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In the tens column!
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So we move it over into our tens column, which
sometimes we call 'carrying,' and now we're
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going to count how many stacks of ten we have.
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We have 1, 2, 3, 4, 5, and then the one that
came over from the ones column - 6.
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We have 6 tens!
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So we write 6 in our tens column.
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We have 6 in the tens column, and 1 in the
ones column: 61.
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32 + 29 equals 61.
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Let's try another problem, but this time let's
pretend that we have boxes of cookies.
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Each box can only fit 10 cookies.
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So first we have 29 cookies, that's 2 boxes
of 10 cookies and 9 individual cookies - and
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we want to add to that 17 more cookies, that's
one box of 10 cookies and 7 individual cookies.
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So we'll start by adding our individual cookies,
because we always start in the ones column.
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Let's count.
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We have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 cookies,
and we're going to stop for a minute and put
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those cookies into a box, then we're going
to count the rest of the cookies.
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We have 1, 2, 3, 4, 5, 6 cookies left.
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So in our ones column, we have one box of
10 cookies, and 6 individual cookies, or 16
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cookies: 9 + 7 equals 16.
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Now we have to move our full box of cookies
out of the ones column and over to the tens
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column with all of the other boxes.
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Then we only have 6 cookies left in the ones
column, so we'll write '6' in our ones column.
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Let's count how many boxes of 10 cookies we
have now!
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1, 2, 3, then the one that came over from
our ones column - 4!
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We have four boxes of 10 cookies, so in our
tens column we write 4.
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So, we have 4 in our tens column, and 6 in
our ones column: 46.
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29 + 17 equals 46.
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Now that you know how to add two digit numbers
together and regroup them, try some problems
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on your own!
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