module 2 lesson 9
TRANSCRIPT
Module 2 Lesson 9 Sums and Differences of Decimals.notebook
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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
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.
Module 2 Lesson 9 Sums and Differences of Decimals.notebook
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Addition / Subtraction Vocabulary
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Fraction to Decimal Review
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Or divide the numerator by the
denominator
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§ 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.
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Example 1
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Example 2
Is the difference is close to the estimation?
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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?
Estimated answer
Actual answer
Expression
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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?
Estimated answer
Actual answer
Expression
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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?
Estimated answer
Actual answer
Expression
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Estimated answer
Actual answer
Expression
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?
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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.
Use a calculator to convert the fractions into decimals before calculating the sum or difference. Divide the numerator by the denominator.
Estimated answer
Actual answer
Expression
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Closing
Please take out your exit ticket for Lesson 9, close your binder, and complete the exit ticket. This will be collected.
Which exercises would be easiest if the addends, minuends, or subtrahends were converted to decimals.