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.