Estimation with Decimals

U03_L2_T3_we1 Estimation with Decimals

Janelle is training
for a road race.

Her pedometer tracks how
far she runs every day.

Here are the pedometer readings
for the past four

days: on Saturday, she went
3.89 miles; Sunday, 5.1;

Monday, 10.21; Tuesday, 3.35.

Estimate the total distance she
ran over the four days,

and then calculate
the exact amount.

Let's estimate first. So I'm
just going to round them to

the nearest mile.

So 3.89, let's round
it up to 4 miles.

And I'm doing that because in
the tenths place, we have an

8, which is 5 or greater.

So let's just make that
roughly 4 miles.

Let's make this 5.1.

We round that down because
this 1 is less than 5.

So let's make this 5 miles.

10.21, let's make that
10 miles because

2 would round down.

It's less than 5.

And 3.35, let's make that 3
miles, because 3 is less than

5, so we'd round down.

So that is 3 miles.

And if we were to add them
up, 4 plus 5 is 9.

9 plus 10 is 19.

19 plus 3 is 22.

So my estimate is that she ran
22 miles over the four days.

That's my estimate.

Now let's figure out the exact
amount that she ran.

Let me scroll down
a little bit.

So we're going to have to add
3.89 to 5.1-- and remember,

when you're adding decimals,
you want to line up the

decimal-- 10.21 and
then finally 3.35.

And let's add all of these up.

Now we'll start in the
hundredths place.

There's nothing here, so 9 plus
nothing plus 1 is 10,

plus 5 is 15.

So let's write the 5, and then
carry, or regroup, the 1.

Let me do this in
another color.

1 plus 8 is 9.

9 plus 1 is 10.

10 plus 2 is 12.

12 plus 3 is 15.

Put the 5 down.

Carry, or regroup, the 1.

1 plus 3 is 4.

4 plus 5 is 9.

9 plus 0 is still 9.

9 plus 3 is 12.

Write the 2.

Regroup this 1 right here.

I'll do it out here just so it's
not part of any of these

numbers, and then
1 plus 1 is 2.

And then we have to remember
the decimal

sitting right over there.

So the exact distance she
ran was 22.55 miles.

So our estimate wasn't
too bad.

It was 22 miles.

We got reasonably close, within
about little over a

half a mile.