September 21, 2011
Estimating Sums
and Differences
1) Review estimating sums and differences of whole
numbers and decimals
Teachers' notes
Lesson objectives
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Teachers' notes
Lesson objectives
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September 21, 2011
Math Words
Round: to find the nearest value of a
number based on a given place
value.
estimate: to find a number that is close
to the exact answer.
Rounding
Ex: Round 14.42 to the nearest tenth
Step 1: Underline the digit to be rounded
14.42
Step 2: Look at the digit to the right.
14.42
Rounding
Ex: Round 14.42 to the nearest tenth
Step 3: If the digit is 5 or greater,
round up. If the digit is less than 5 the
value stays the same and you drop
the numbers after it.
14.42 = 14.4
September 21, 2011
Round to the nearest ten:
2,378
Round to the nearest hundredths:
6.955
Round to the underlined place.
7,560 _________
$2,215.42 _________
11.029 _________
9.3069 _________
28.4413 _________
September 21, 2011
Estimating sums or differences
Step 1: Round each number first.
Step 2: Round whole numbers to the
largest place value.
6,138
+7,315
Step 3: Round decimals to the nearest
ones
8.23
-1.87
Estimating sums and differences
Step 4: Add or subtract the
rounded numbers.
6,000
+7,000
More Examples
8
-2
September 21, 2011
You Try!
33.56
+ 0.67
40.23
+30.46
25.21
- 22.843
$116.86
+ 54.31
Independent/ small group
TB pg.24 #'s 20-44
Extra Practice:
Homewok: PB pg.7