Singapore Math: Grade 3a Unit 2 (part 7) Video Lecture | Mathematics Lesson for Grade 3 (Singapore) - Personal Learning

let's do a couple more examples of
adding four-digit numbers so let's say I
have three thousand five hundred and
eighty-nine three thousand five hundred
and eighty nine plus plus that's a plus
two thousand four hundred and forty
three so let's write it down in the
place notation first let's do the three
thousand five hundred eighty nine maybe
I'll do them in different colors that
always I think help so I'll do the two
thousand four hundred and forty three in
this color when is this magenta 43 so
2005
sorry 3580 now is through the top one
first so we have three thousands so
let's say it's one thousand two thousand
three thousand five hundred one two
three four five each of these are a
hundred give you them as a hundred
dollars or if you gamble they could be a
poker chip worth $100 not that I
encourage you to gamble and the eight
tens so let's see one two three four
five six seven eight
each of these are ten and you really
don't I mean you you it might be fun to
do this every now and then but if you're
taking a test you shouldn't have to do
this I'm doing this so that you really
understand what happens when we regroup
numbers or when we carry the one so to
speak that's the way I learned it when I
first learned how to add and I had
multi-digit numbers and then we have
nine ones one two three four five six
seven eight nine and you should these
are one so that's three thousand five
hundred eight nine eight 10s and nine
ones three thousand five hundred eighty
nine and now let's do the 2443 so we
have two thousand one thousand two
thousand that's the house right there
400
one two three four hundred each of these
are a hundred then we have four tens one
two three four each of those are ten we
have three ones one two three now we are
ready to add now that we've drawn
everything so let's go to the ones place
I'll do it in a different color here so
you have 9 plus 3 9 plus 3 is 12 we
can't put a 12 in the ones place so the
way that we learn how to do it is we
said well a 12 is essentially 10 plus 2
right 9 plus 3 is the same thing as 12
which is 10 plus 2 well 10 plus 2 we can
write the 2 here and then the 10 we can
put it into the tens place and that
looks just like we said 9 plus 3 is 12
but essentially we're saying 9 plus 3 is
10 plus 2 but you can do it either way I
mean once you're actually as long as you
understand what you're doing
feel free to say 9 plus 3 is 12
especially when you have to do it fast
and what did we just do in reality well
we said we have how many ones do we have
we have 1 2 3 4 5 6 7 8 9 plus 3 10 11
12 and what we did is we took 10 of
these we took 10 of these and we
converted them to another 10
all right and so you could almost view
them as you know they're no longer in
the ones place I I put them all in a
canister or I exchanged them all for a
$10 bill and I put them in the tens
place and then I only had two left in
the ones place and that's exactly what
we did here two left in the ones place
and the other 10 I exchanged for one in
the tens place all right so let's see
what happens in the tens place I have 1
2 3 4 5 6 7 8 9 10 11 12 13 tens so 13
tens well that's the same thing as 10
tens plus 3 tens right so why don't I
take 10 of the tens and convert them to
100 so let's see let me do that 1 2 3 4
5 6 7 8 9 10 let me take 10 of these and
I'm gonna create a hundred out of them
so they're not no longer in the tens
place and how do I do that here well I
say that 1 plus 8 plus 4 is 13 well I
can only put the 3 so it's 13 tens well
that's the same thing as three tens
right that's these three tens one two
three that's the same thing as three
tens and 100 and that hundred right I
took I took out 10 of the tens from here
but I and I converted them into a
hundred and that's all I did and you
know once again if you're doing if
you're if you're just doing this quickly
you just have to say a 1 plus 8 plus 4
is 13 1 3 that's 13
but and I know I'm being very very
repetitive but you really should
understand what you're doing why this
works and that's why I'm going through
this long arduous explanation of
converting 10 of these tens to a hundred
and that's why that one shows up well
anyway let's go to the hundreds place
how many hundreds do we have we have 1 2
3 4 5 6 7 8 9 10 hundreds right and if
you look at it this way 2 we have 1 plus
5 plus 4 is 10 so let's take all of
these hundreds and I'll arbitrarily
switch colors now let's take all of
these owners because you can't write a
10 in any one place 10 isn't
10 is a two-digit number let's convert
10 hundreds into a thousand so that
becomes a thousand and so we got rid of
everything in the hundreds place so
essentially we have zero hundreds but we
have an extra thousand so we have zero
hundreds and an extra a thousand and the
way we could have done that we could've
said one plus five plus four is ten but
this is what we actually did we said
that well it could be ten hundreds or
zero hundreds and one thousand that's
the intuition and now we're almost done
how many thousands do we have one two
three four five six thousands or one
plus three plus two is six so the answer
is six thousand and thirty-two let's do
a bunch of quick problems and this time
I won't draw this out but you shouldn't
just mechanically say oh I'm carrying
the one or I'm regrouping the one or
whatever you should really understand
what's going on when when we when we you
know and we put this one up here every
time let's do some problems it's amazing
how many people will go through life and
they will be carrying their ones and
they they and these are smart people but
they never take the time to understand
why the carrying the one works and
really especially in mathematics and in
science but really in all things in life
you should never take things at face
value you'd be amazed how much of well
you know think about think about 50
years ago how much people thought was
true that that now we know is isn't true
especially you know a lot of fields like
medicine and and even in physics or
wherever else so so even the things that
are being taught to you today in 50
years some of it might be proven to be
false so that's why it's very very
important that you always make sure you
understand why something works you just
don't take it as you know as faith that
it's going to work and that way when you
prove a different way of doing it
because you really understand how things
work you'll get a Nobel Prize and you'll
be famous and you can say that sounds
videos I edit for this Nobel Prize and
anyway let's go back to the math so
what's 7 plus 6 it's 13 right
thirteen well we could just say well
thirteen one three but what did we
really do we said seven plus six is
three ones and one ten and that's
essentially what 13 is right if we just
write down the number thirteen that says
it that tells us it's one ten and three
ones and we just floated here one ten
and three ones then we say 110 plus nine
tens plus 110 that's eleven tens right
eleven tens well eleven tens is the same
thing as one 10 and 100 right 110 but
you know if you're just doing this fast
you say one plus nine plus one is eleven
and then you're at one one and then you
say one plus six plus three what is that
that is ten well we're in the hundreds
place so ten hundreds you could also
write that as zero hundreds and one
thousand right ten hundreds is a
thousand and we have one plus four plus
one is six not too bad
let's do another one three thousand five
hundred and eighty seven plus three
thousand eight hundred and thirteen ten
plus 3 is 10 well you can't put a 10
here it's essentially just zero ones and
1 10 and that's what 10 is I mean when I
write 10 that's telling me to have one
10 and zero ones anyway I think I'm
being repetitive all right one plus
eight plus one well that's 10 again so
but since we're in the tens place that's
10 tens right so that's equal to 100 and
zero tens we convert them all for 100 1
plus 5 Plus 8 that's what that's 14 but
it's actually 14 hundredths right
because we're in the hundreds place so
1400s that's the same thing as four
hundred and one thousand right and then
one plus three plus three that's seven
we're in the thousands place with seven
thousand seven thousand four hundred is
our answer let me arbitrarily switch
colors and arbitrarily means that I'm
doing it for no good reason
except for
except to just switch colors because it
looks nice five eight nine - okay and
this time I'm just going to go through
it just show you how fast you can do it
I'm not going to keep explaining that oh
you know a thirteen is three ones and a
1/10 and so that's why we carry it I'm
just going to do it so 8 + 2 0 ones 1 10
or 10 1 + 9 right or 10 + 90 that's a
hundred so it's zero tens and 100 one
plus nine plus eight that's 18 right but
we're in the hundreds place was 1800s so
that's eight hundreds it's 1,000 and
then we have one plus two plus five is
eight thousands let's do one more
problem in a different color
2824 plus two thousand five hundred and
seventy six that's a 6 4 plus 6 is 10 1
plus 2 plus 7
well that's 10 again 1 plus 8 is 9 plus
5 is 14 1 plus 2 plus 2 that's five
5,400 and so you know you can see that I
carried it but just remember that when I
when I carry the 1 I'm essentially
saying you know like for example when I
say 4 plus 6 it equals 10 that's 0 1 + 1
10 and that's why I put the 1 in the
tens place anyway I will see you in the
next video where we will do 4 digit
subtraction see you soon