1. Module 2 Lesson 9 Sums and Differences of Decimals.notebook
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December 10, 2014
MODULE 2 Arithmetic Operations Including
Division of Fractions
Topic B: Multi‐Digit Decimal Operations—Adding,
Subtracting, and Multiplying
Lesson 9: Sums and Differences of Decimals
Aug 26­5:
45 PM
Student Outcomes
§ Students relate decimals to mixed numbers and round addends, minuends,
and subtrahends to whole numbers in order to predict reasonable answers.
§ Students use their knowledge of adding and subtracting multi‐digit numbers
to find the sums and differences of decimals.
§ Students understand the importance of place value and solve problems in
real‐world contexts.

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December 10, 2014
Addition / Subtraction Vocabulary
Nov 17­2:
28 PM

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Fraction to Decimal Review
Nov 17­2:
29 PM

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Nov 17­2:
29 PM
Or divide the
numerator
by the
denominator

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December 10, 2014
§ Can you describe the circumstances when it would be easier to
add and subtract mixed numbers by converting them to decimals
first?
ú When fractions have large denominators that would make it
difficult to find common denominators in order to add or subtract.
ú When a problem is solved by regrouping, it may be easier to
borrow from decimals than fractions.
§ How can estimation be used to help solve addition and
subtraction problems with rational numbers?
ú Using estimation can help predict reasonable answers. It is a
way to check to see if an answer is reasonable or not.
Nov 17­2:
29 PM

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December 10, 2014
Nov 17­2:
29 PM
Example 1

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December 10, 2014
Nov 17­2:
29 PM
Example 2
Is the difference is close to the estimation?

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December 10, 2014
1. Samantha and her friends are going on a road trip that is miles long. They have already
driven . How much further do they have to drive?
Nov 17­2:
28 PM
Expression
Estimated answer
Actual answer

9. Module 2 Lesson 9 Sums and Differences of Decimals.notebook
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December 10, 2014
Dec 10­8:
22 AM

10. Module 2 Lesson 9 Sums and Differences of Decimals.notebook
December 10, 2014
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2. Ben needs to replace two sides of his fence. One side is meters long,
and the other is meters long. How much fence does Ben need to buy?
Nov 17­2:
28 PM
Expression
Estimated answer
Actual answer

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December 10, 2014
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3. Mike wants to paint his new office with two different colors. If he needs
gallons of red paint and gallons of brown paint, how much paint does he
need in total?
Dec 15­1:
31 PM
Expression
Estimated answer
Actual answer

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December 10, 2014
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4. After Arianna completed some work, she figured she still had pictures to
paint. If she completed another pictures, how many pictures does Arianna still
have to paint?
Dec 15­1:
31 PM
Expression
Estimated answer
Actual answer

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Use a calculator to convert the fractions into decimals before calculating the sum or
difference. Divide the numerator by the denominator.
Rahzel wants to determine how much gasoline he and his wife use in a month. He
calculated that he used gallons of gas last month. Rahzel’s wife used
gallons of gas last month. How much total gas did Rahzel and his wife use last
month? Round your answer to the nearest hundredth.
Dec 15­1:
31 PM
Expression
Estimated answer
Actual answer

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December 10, 2014
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Which exercises would be easiest if the addends,
minuends, or subtrahends were converted to
decimals.
Aug 26­8:
21 PM
Closing
Please take out your exit ticket for Lesson 9, close your
binder, and complete the exit ticket. This will be collected.