Singapore Math: Grade 3a Unit 2 (part 6) Video Lecture | Mathematics Lesson for Grade 3 (Singapore) - Personal Learning

let's keep adding some four digit
numbers see I'm one page 25 of the
Singapore Math three a book and we're
going to do problem number three let me
actually draw the the places like I've
had the last couple of problems so let
me draw some columns some line some
separators so so I'll do the one space
to the right of that 10 space and this
for the hundreds and thousands and the
left with that I can actually write the
problem let me write down this is
thousands this is hundreds this is tens
this is ones ok so the problem we have
here is 5840 5840 and let's write that
out into the bucket so we have five
thousands and thousands place we have
five so that's 1 2 3 4 5 i'm going to
stop writing a thousand and every one of
those you know that these are each worth
a thousand we have 800 so one two three
four five six seven eight hundreds and
you know each of those are worth 100 we
have four tens one two three four tens
and we have zero ones fair enough no
one's actually I I enjoy writing a
thousand here so I'm going to do it
there's no space to ride 100 each of
those but you know that you could cash
these in for a hundred dollars you can
catch each of these in for ten thousand
and a thousand and we are going to add
that to 60 so it's plus 60 so 60 that's
six tens so we have let's see I could do
it down here 1 2 3 4 5 6 10 and 0 ones
and that's all there is so let's see if
we can add it up so what's 0 plus 0 0
plus 0 is 0
oh and now how many tens are there well
if we add 4 plus 6 we get 10 you can't
write a two digit number in the tens
place so what we're going to do is we're
going to get take it take 4 plus 6 is 10
and convert that entire 10 to 100 and
how can I do that because this is the
tens place right so this is for tens
plus 6 10 s is equal to 10 10 10 tens is
equal to 100 or you could say 40 plus 60
is equal to 100 and so if we converted
all of the the tends to 1 100 we have no
tens here and we have an extra 100 and
could visually view it this way where we
have one two three four five six seven
eight nine ten tens right and what I
just did is I took all of those I took
all of those tens and I converted them
into a hundred all right 100 in there
and then I had no tens leftover they
were all converted and that's exactly
what I did here I said this for tens
plus this 66 x is equal to 10 tens let
me convert them all into one hundred
this is 100 so you could view this 100
as this one up here and then I have no
10s left over and that's that's zero and
then I'm in the hundreds place 100 plus
800 is 900 and we could count that one
two three four five six seven eight nine
and then we have five thousand so you
get 5900 let's do another problem let me
see if I can erase all of this without
having to redraw everything that was
pretty good if I can do something that's
pretty good let's see if I can do with
it here yes I'm getting good at this
I'll clean this up a little bit that's
about as good as I can expect and then
on this end let's see how well I can
look at that that was neat ok so the
next problem we have is the next problem
is 3700 or 3000
100 plus 300 and think about this in
your head right and I kind of gave you a
hint I mean you really should pronounce
this is 3700 or you could pronounce this
is 3700 but either way what's 37 plus 3
well 37 plus 3 37 plus 1 is 38 37 plus 2
is 3937 plus 3 is 40 right so you
probably have an intuition already that
this is going to equal 4,100 or 4,000
but anyway if that confuses you ignore
it I'm going to draw it out with a place
notation so we have three thousands in
this top number so there's three
thousands right here that's one two
three each of those are worth a thousand
and I have seven hundreds one two three
four five six seven each of these are
worth 100 and i have no tens and no ones
and then in this bottom number i'll see
i have three hundreds and that's all i
have i just have three hundreds so let
me add it here one two three so let's
add 0 plus 0 0 plus 0 is 0 0 plus 0 0
and as we can see we have no one's know
tens and so that makes sense and then 7
plus 3 is 10 and what we can do this is
700 + 300 right so 700 + 300 is a
thousand so instead of right you can't
write a thousand down here so let's
convert those 10 hundreds into a
thousand so let me do this in a new
color a little bit in bold red and then
we have no hundreds left so how do we
think about that here well we hit 700 +
300 so we have one two three four five
six seven eight nine ten what we do is
we take all of them we're going to take
those ten hundreds and convert it into a
thousand and then since we converted we
have no hundreds left right so we have
no hundreds left
we converted them all into a thousand so
this thousand is the same thing as this
one here up in the thousands place so we
have a 1000 plus three thousand one
thousand plus three thousand it is equal
to four thousand so that is exactly what
we thought about when we said well what
30 37 plus three is 40 but we're saying
3700 plus 300 is 40 hundred or four
thousand and if you wanted to just do
this mechanically you could have just
said thirty seven hundred plus 300 you
can just 80 0 that's not what I wanted
to do that's not what I wanted to do we
could say 0 plus 0 0 0 plus 0 0 and this
is kind of traditional white people are
going to do it they say 7 plus 3 is 10
and they say well 10 let's write the 0
carry the 1 and then 1 plus 3 is 4 but I
don't like that carrying away in the
singapore math curriculum doesn't like
the caring way because you don't know
why you carried it you don't know why
you wrote the 0 from the 10 you wrote
the one there what you actually did is
you said 7 plus 3 is 10 you can't write
a 10 here so let's convert that entire
10 into one of the next place right so
yeah this is 700 + 300 is equal to ten
hundred or a thousand and then you have
none of the and then you have none of
the hundreds left because you convert it
all to a thousand and you have 1000 +
3000 is 4000 so let's do a bunch of
problems this is where on page 26 now
and I won't draw it out the place value
but you should think about it in your
head that the place value is happening
so the first problem we have is 1028
plus 234 so what's 8 plus 4 it's 12 we
can't put a 12 in the ones place so
let's just take out of that 12 let's
take ten and convert it to a 10 and then
we would just have two left over and you
could if you wanted to do this you know
in a mechanical way you could say eight
plus four is twelve carry the one but
what we really did it said eight plus
four is twelve of the 12 we're going to
put two
in the ones place and then take 10 and
convert it to a 10 and then we have 110
plus 2 10 s plus 3 tens that's six tens
right zero hundred plus 200 is 200 and
then one so 1262 let's do another one
and i will switch colors for variety
2409 plus 1245 what's 9 plus 5 well 9
plus 5 is 14 we can only write one digit
here so out of the 14 let's write the
four and then the remain the rest of the
10 let's convert it into a tens place or
put it in the tens place so this one
represents 10 and this is the four so 10
plus 4 is 14 that's all we did or you
could say 9 plus 5 is 14 but you should
be understanding why we're doing this
it's not just some kind of you know
random game we're doing it should all
make sense in your head that this you
know that this isn't some kind of magic
and so we have 110 plus 0 10 s plus 4 10
so 10 plus 40 is 5400 plus 200 is 600
2000 plus 1000 is 3,000 so it's 3654
let's do another one and I'll keep
switching colors 4190 plus 649 so what's
0 plus 9 that's easy that's just nine
what's 9 plus 4 it's 13 or we could view
it as 90 plus 40 s 130 but 9 plus 4 is
13 we could put the three here and then
convert the 10 into one of the next
decimal place so another way of view it
is 90 plus 40 is 30 and 100 right and
the hundred we write in the hundreds
place 100 plus 100 plus 600 is 800 or
one plus one plus six is eight and then
you bring down the four thousand four
thousand plus 0 is 4
so it's 4839 let's keep going I think
we're on a roll what problem are we on
so three thousand two hundred and sixty
plus 4280 20 plus two is 26 plus eight
is 14 let's put the four here and then
the 10 let's put it in the next place
and does that make sense well 60 plus 80
is 140 so this is this represents the
hundred and this represents the 40 right
if it's 100 let's put it in the hundreds
place a 1 in the hundreds place
represents 100 so one plus two plus two
that's five but these are really
hundreds right for the hundreds place
and three plus three thousand plus four
thousand is 7,000 let's do two more
problems I might be running out of
colors soon 6204 plus 993 what's four
plus three that's seven what's 0 plus 9
plus 9 what is 200 you know this is zero
tens this is 90 right so it's 90 what's
what's 200 plus 900 it's 1100 you could
say so let's 1,100 is the same thing as
1100 so let's rewrite it as 1100 that's
all I did or you could say 2 plus 9 is
11 but we're really doing is saying that
200 plus 900 is 1100 so 1000 plus six
thousand is 7,000 and we could have
written this one anywhere we just ride
it all the way up on top just because
it's neat if we wrote it like here we
would get it confused with other things
so that's the reason why it goes all the
way up here there's nothing special
about its position let's do one last
problem for this video I know I'm
running
long so it's 5402 plus 2962 plus zero is
20 10 s plus six tens is six tens or
sixty four hundred plus 900 is 1300 1300
is 1000 so put the one in the thousands
place and 300 right 1,000 plus 5,000
plus 2,000 is 8,000 8,000 362 I'll see
you in the next video