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Find the sum of negative 15 plus
negative 46 plus negative 29.
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To do this, let's
just first visualize
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what each of these
numbers look like.
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So I'm going to draw a
number line for each of them.
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Negative 15 might look
something like this.
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So if this is 0 and let's
say that this is negative 15,
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I could represent
negative 15 as--
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if I'd like to-- an arrow that
points from 0 to negative 15.
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The length of the arrow is
the absolute value of this.
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It's the distance from 0.
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So the length here is 15.
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And the negative says that
we are pointing to the left.
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So the absolute value is 15.
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That's the length of that arrow.
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Let's do the same
thing for negative 46.
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So once again, let me
draw my number line.
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0 is going to be
right over there.
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And negative 46 is going
to be someplace over here.
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Negative 46.
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Notice, same exact idea.
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The distance between negative
46 and 0-- or another way
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to think about that is the
absolute value of negative 46--
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this distance right over
here is going to be 46.
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And its direction
is to the left.
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That is why we get to
the number negative 46.
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The negative really tells you
whether you're to the left
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or to the right of 0,
but the absolute value
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says how far are you to
the left or the right of 0.
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And then, finally, let's do
the same thing for negative 29.
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So once again, let me
draw my number line.
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I want to use the yellow again.
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So draw my number line.
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Let's say this is 0.
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Then negative 29 is going
to be roughly over here.
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I'm estimating it.
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And once again, negative 29
is exactly 29 away from 0.
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So this length right over here
is 29, and it is to the left.
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That is why it is negative 29.
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If it was positive 29, it
would be 29 to the right of 0.
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So we've represented
all of these numbers.
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And you can see what their
absolute values are like.
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And now let's think about
what happens if you add them.
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So one way to think about
adding these numbers
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is if you added
these arrows, if you
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put this arrow on
top of this arrow
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or to the left of this
arrow, if you started where
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this arrow leaves off-- and
then you put this green arrow,
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and then you put
the orange arrow.
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So let's do that.
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Let's draw that.
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It's going to be a
longer arrow now.
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So we're going to start at 0.
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First, we have the negative 15.
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So we're going to move
15 spaces to the left
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to get us to negative 15.
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Then we're going to go
46 spaces to the left
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to get us to negative
15 plus negative 46.
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So let me draw that.
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So then we're going
to go-- and we're
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going to figure out what
that number is in a second.
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So then we're going
to go 46 to the left.
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That's about that far.
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Really just this arrow,
I'm now placing it.
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I'm starting off where
the negative 15 left off,
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and then I'm putting
that arrow after that.
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And we don't know yet what
number this gets us to.
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We're going to have to
do a little math here.
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And that's actually the
point of this problem.
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But we know what the
length of this arrow is.
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The length of this arrow is 46.
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It is 46 to the
left, and we know
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the length of this
magenta arrow is 15.
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And then, finally, we
have this orange arrow.
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The orange arrow, which we
know has a length of 29.
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Although, it's 29 to the left.
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It looks like that.
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It has a length of 29.
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So when all is said
and done, where are we?
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Where do we end up
on our number line?
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Well, the total length
that we are to the left
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is going to be 15
plus 46 plus 29.
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But it's going to
be to the left,
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so it's going to be negative.
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So what we can really view
this as, since all of these
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have the same sign,
is we could say,
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look, this is the same
thing as the absolute value
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of negative 15, which is
15, plus the absolute value
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of negative 46, which is
46, plus the absolute value
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of negative 29,
which is 29, but then
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take the negative value of it.
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So let's just add that.
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15 plus 46 plus 29 is equal
to, let's see-- 5 plus 6 is 11.
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11 plus 9 is 20.
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Carry the 2.
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2 plus 1 is 3.
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3 plus 4 is 7.
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7 plus 2 is 9.
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So you get 90.
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So this entire
length here is 90.
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The entire length, if you add
up the arrows, you get a 90.
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But it is not 90 to the right.
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So if it was 90 to the right,
these would all be positives.
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And then we would just
get a positive 90.
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But this is 90 to the left.
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So when you add these guys up,
you don't get to positive 90.
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You get to negative 90.
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So one way to think about it
is these are all the same sign.
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So this is going to be
equal to the negative
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of the absolute
value of negative 15
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plus the absolute
value of negative 46
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plus the absolute
value of negative 29.
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And the reason why we're
writing this here-- this
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might look fancy,
but this is really
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just the length of
this purple arrow.
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This absolute value
of negative 46,
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that's really just the
length of the green arrow.
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46.
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And this is just the
length of the orange arrow.
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So this is 15 plus 46
plus 29, gave us 90,
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but it is to the left.
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So that is why it
is negative 90.
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