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Janelle is training
for a road race.
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Her pedometer tracks how
far she runs every day.
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Here are the pedometer readings
for the past four
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days: on Saturday, she went
3.89 miles; Sunday, 5.1;
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Monday, 10.21; Tuesday, 3.35.
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Estimate the total distance she
ran over the four days,
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and then calculate
the exact amount.
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Let's estimate first. So I'm
just going to round them to
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the nearest mile.
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So 3.89, let's round
it up to 4 miles.
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And I'm doing that because in
the tenths place, we have an
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8, which is 5 or greater.
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So let's just make that
roughly 4 miles.
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Let's make this 5.1.
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We round that down because
this 1 is less than 5.
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So let's make this 5 miles.
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10.21, let's make that
10 miles because
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2 would round down.
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It's less than 5.
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And 3.35, let's make that 3
miles, because 3 is less than
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5, so we'd round down.
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So that is 3 miles.
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And if we were to add them
up, 4 plus 5 is 9.
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9 plus 10 is 19.
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19 plus 3 is 22.
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So my estimate is that she ran
22 miles over the four days.
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That's my estimate.
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Now let's figure out the exact
amount that she ran.
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Let me scroll down
a little bit.
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So we're going to have to add
3.89 to 5.1-- and remember,
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when you're adding decimals,
you want to line up the
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decimal-- 10.21 and
then finally 3.35.
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And let's add all of these up.
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Now we'll start in the
hundredths place.
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There's nothing here, so 9 plus
nothing plus 1 is 10,
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plus 5 is 15.
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So let's write the 5, and then
carry, or regroup, the 1.
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Let me do this in
another color.
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1 plus 8 is 9.
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9 plus 1 is 10.
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10 plus 2 is 12.
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12 plus 3 is 15.
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Put the 5 down.
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Carry, or regroup, the 1.
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1 plus 3 is 4.
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4 plus 5 is 9.
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9 plus 0 is still 9.
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9 plus 3 is 12.
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Write the 2.
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Regroup this 1 right here.
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I'll do it out here just so it's
not part of any of these
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numbers, and then
1 plus 1 is 2.
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And then we have to remember
the decimal
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sitting right over there.
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So the exact distance she
ran was 22.55 miles.
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So our estimate wasn't
too bad.
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It was 22 miles.
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We got reasonably close, within
about little over a
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half a mile.
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