Lesson 1
Understand
Mental Math Strategies (Fact Families)
Name: How can adding help you subtract?
Study the example showing how adding helps
you subtract. Then solve Problems 1–7.
Example
Solve 9 2 5.
Make a number
bond.
9
Write an addition
problem. Solve.
Then solve the
subtraction.
51?59
92554
51459
5
1
?
Circle the number bond for 13 2 6.
13
6
2
?
?
13
6
Complete the number bond. Write four
number sentences.
1 5 13
13 2 5 13 5 1 5 13 2 ©Curriculum Associates, LLC Copying is not permitted.
13
6
Lesson 1 Understand Mental Math Strategies (Fact Families)
3
Solve.
3
Complete the number bond to show
15 2 6 5 ? .
15
6
4
Write an addition sentence for the
number bond in Problem 3. Then
complete the subtraction sentence.
1 5 15 2 6 5 5
Complete the number bond to show
16 2 7 5 ? .
6
Write the fact family for the number
bond in Problem 5.
1 5 1 5 2 5 2 5 7
Show how to find 14 2 8 5 ? using
addition.
Show your work.
Vocabulary
fact family a group of facts that
all use the same
three numbers.
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Lesson 1 Understand Mental Math Strategies (Fact Families)
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Lesson 1
Name: Use Different Strategies to Subtract
Study how the example shows counting on to
subtract in your head. Then solve Problems 1–6.
Example
13 2 9 5 ?
Think of it as 9 1 ? 5 13.
9
10 11
12
13
Count on to get from 9 to 13.
The marks show how many you counted on.
1
Solve the addition problem.
9 1 4 5 13
Solve the subtraction problem.
13 2 9 5 4
Fill in the blanks in each number sentence.
9 2 4 5 ? is the same as 1 ? 5 .
11 2 7 5 ? is the same as 1 ? 5 .
8 2 3 5 ? is the same as 1 ? 5 .
15 2 8 5 ? is the same as 1 ? 5 .
2
Choose one subtraction number sentence
from Problem 1. Do you think it is faster to
solve it using addition facts or counting on?
Explain.
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Lesson 1 Understand Mental Math Strategies (Fact Families)
5
Solve.
3
Fill in the blanks in the number sentence.
12 2 7 5 ? is the same as 1 ? 5 .
4
Fill in the number bond to find
12 2 7 5 ? . Then write your answer.
12 2 7 5 5
Show a different way to find 12 2 7.
Show your work.
12 2 7 5 6
In Problems 4 and 5 you used two
different strategies to find 12 2 7 5 ? .
Which strategy do you think is faster to
do in your head? Explain.
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Lesson 1 Understand Mental Math Strategies (Fact Families)
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Lesson 1
Name: Reason and Write
Look at the example. Underline a part that
you think makes it a good answer.
Example
Choose a problem.
9 2 6 5 ? 12 2 4 5 ?
14 2 5 5 ? 15 2 8 5 ?
1.Show how to solve the problem by
drawing a picture of an open number
line.
2.Explain how to use the number line to
solve the problem.
Show.
Where does the
example . . .
12 2 4 5 ?
2
8
• show the
selected
problem?
2
10
• show the
strategy?
12
Explain.
I pictured an open number line. I started with 12.
• explain the
strategy?
First I subtracted 2 to make 10. Then I subtracted
2 more to subtract a total of 4. Since I ended up
on 8, I know that 12 2 4 5 8.
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Lesson 1 Understand Mental Math Strategies (Fact Families)
7
Solve the problem. Use what you learned from the example.
Choose a problem.
9 2 6 5 ?11 2 3 5 ?
14 2 5 5 ?15 2 8 5 ?
1.Show how to solve the problem by
drawing a picture of an open number
line.
2.Explain how to use the number line to
solve the problem.
Show.
Did you . . .
• show the
selected
problem?
• show the
strategy?
Explain.
• explain the
strategy?
8
Lesson 1 Understand Mental Math Strategies (Fact Families)
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