Transcript Estimating Sums and Differences with Whole Numbers

Estimating Sums
and Differences
with Whole
Numbers
Why do we
estimate?
When do we
estimate?
There are
several ways
to estimate.
1. Rounding
• Rounding makes numbers that are easier
to work with in your head.
• Rounded numbers are only approximate.
• An exact answer generally can not be
obtained using rounded numbers.
• Use rounding to get a answer that is close
but that does not have to be exact.
1. Rounding
• Find the number in its spot.
Go next door and see what you've got.
5 or more raise the score,
4 or less let it rest.
All the numbers to the right run to zero in
a fright.
6,403,581
1. Rounding
• Some problems will tell you what place to
round to.
• Round to the nearest thousand.
126,965
193,210
• When adding or subtracting, round to
the highest place value of each number
126,965+193,210=_________ estimate
http://www.funbrain.com/tens/index.html
2. Front End Estimation
• Front end estimation mostly produces a
closer estimate of sums or differences
than the answer produced by adding or
subtracting rounded numbers.
2. Front End Estimation
1. Look at your math problem.
2. Do both numbers have the same amount of
digits?
3. 5,467+326=______
4. The number with the least amount of digits
sets where you would estimate.
5. Change all numbers behind that number to
0.
http://superteacherworksheets.com/addition/a
ddition-3dig.pdf
3. Compatible Numbers
• Compatible numbers for addition and
subtraction are numbers that go together
easily to make nice numbers.
3. Compatible Numbers
• Find numbers that work well together.
• Tina has 6 tomatoes, Miriam has 2
tomatoes and Liam has 3 tomatoes.
They use 9 tomatoes for a salad. How
many tomatoes are left?
3. Compatible Numbers
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•
•
•
•
•
•
•
5 + 2 + 5 – 10
9 + 5 +1 – 6
8+2+7–9
4+5–9
3+5+5–8
4+6+4+3–7
4+2+5–9
8+5+2–7