Rounding whole number word problems | 3rd grade math (TX TEKS) | Khan Academy

- [Instructor] If we're
told a national park

rounded the number of
cars entering the park

on a given date of 6,780 cars,

how many cars could have entered the park

if they rounded the
number to the nearest 10?

Choose all the answers that apply.

So pause this video, try
to solve this yourself

before we solve this together.

Okay, so there's a couple of
ways we could think about it.

We could think about
all of the numbers that,

if you round to the nearest
10, would round to 6,780,

or we could round each of
these to the nearest 10,

or we could do some type of a combination.

Actually, let's do a little
bit of a combination here.

So let's draw a number line,

and so if this right over here is 6,780,

and I'm going to go up
by 10 and down by 10,

since we're rounding to the nearest 10,

so if we go up by 10, this would be 6,790,

and if we go down by
10, this would be 6,000,

I should put a decimal there,
I should put a comma, 6,770.

Now, before I even look at these choices,

what's going to round to 6,780?

Well, if I get to 6,775 right over here,

so this right over here is
6,775, that would round up,

if we're rounding to the
nearest 10, to 6,780.

It's right in between, but the convention,

the rule is that we
round up, and actually,

let me make it, I know
that this isn't exact,

since I'm drawing it, but lemme
make it a little bit closer

to the middle right over here.

So if we're right there, if
we're right there at 6,775,

that's going to round up to 6,780,

and that's going to be
true all the way up to,

but not including, and lemme
put an open circle here,

this right over here is 6,785.

So 6,785 would round up to 6,790,

but if you're right below that,

even just a little bit below,
you would round down to 6,780.

So let's look at these choices and think

about which of these
are on this orange part

of the number line.

So 6,778 cars.

Well, that's going to
be right around there,

and so we clearly see here
that it's in that orange.

It's much closer to 6,780
than it is to 6,770,

so this one works.

It would round to 6,780.

What about 6,774 cars? Well,
that's right over here.

Actually, lemme do this
in a different color

so we can keep track of things,

so this one is right over here,
and you could visually see,

or you can numerically see,
it's closer to 6,770 than 6,780.

It's also out of this orange
area that we talked about,

so we can rule this one out,
and then last but not least,

6,783 is right around there,

and we could see that the two choices,

you could round down to
6,780 or round up to 6,790,

but it's much closer to 6,780.

It's also in this orange area.

It doesn't even quite get halfway yet,

so this one also would round to 6,780.

Let's do another example
problem involving rounding.

So this one tells us

that a school fundraiser collects $3,152.

Round the money to the nearest hundred,

so again, pause the video
and try to work this out.

Well, the way I'm going to do it

is I'm gonna set up a number
line again, and I'm going to,

if I think about the hundreds around this,

I could go the nearest
hundred below this is 3,100,

so this is 3,100, I guess
we're talking about dollars,

and then the hundreds above this is 3,200,

so I'll put that here, so this is $3,200.

Now, we're looking at 3,152,

which is gonna be a little bit more

than halfway towards 3,200,

so that might already show you
the direction we're going in,

but just to make sure
we know what's going on,

if we go anywhere, if
we're above 3,100 up to,

but not including 3,150,
so right over here,

right over here, these are the things,

and there'll be some stuff below here,

but this is the stuff that would-

And this is 3,150, which
is right in between.

If we're at 3,150, you don't round down,

you round up to 3,200, but
if you're at all below that,

if you're at 3,149, you would round down

to the nearest hundred, down to 3,100.

Now, this number is
clearly larger than that.

3,152 is going to be right over here.

It's a little bit larger,
so this one is going

to be a little bit more than
halfway from 3,100 to 3,200,

and you could also see
it's larger than 3,150,

and we would round anything
from 3,150 all the way to 3,200,

almost to 3,250, but not quite 3,250,

we would round that to 3,200,

and so round the money
to the nearest hundred,

this would be 3,200.

If you wanna think about it visually,

whichever hundred it's closer to,

and this is a little bit closer to 3,200

than it is to 3,100, and
if you're right in between,

if you're at 3,150, the rule is,

the convention that
mathematicians have created,

is that you would round up,

but this isn't even right in between.

It's a little bit closer to 3,200.