Lesson 1
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Adding in Any Order
You can add numbers in any order. The sum is the same. This is the commutative property of addition.
Example
The numbers that you add are called addends.
The order of the addends does not matter.
The sum does not change.
Solve
Add. Write the sum.
Write the missing number.
Chen and Alex see 1 cat and 3 dogs. They count to see how many animals in all. Chen counts the dogs first and then the cat. Alex counts the cat first and then the dogs. Are the sums different? Explain.
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Lesson 2
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Grouping Numbers to Add
You can add three addends. Group the numbers first.
Examples
Solve
Show two ways to group the addends. Use ( ).
Add. Be sure to add the numbers in ( ) first.
Lesson 3
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Subtracting
You can use place value to subtract.
Example
The answer to a subtraction problem is called the difference.
Solve
Subtract.
Read the problem. Decide if you should add or subtract to solve it. Explain how you know.
Damon has 15 balloons. He pops 4. How many balloons are left?
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Lesson 4
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Finding a Missing Addend
Subtract to find a missing addend.
Example
Solve
Subtract. Write the difference. Then write the missing addend in the box.
Read the problem. Write the addition sentence you would use to help find the missing addend.
Uma and John planted 8 seeds. Uma planted 3 of the seeds. How many seeds did John plant?
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Lesson 5
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Fact Families
Some addition and subtraction facts use the same numbers. They make up a fact family.
Example
This fact family uses the numbers 4, 5, and 9.
Solve
Complete the fact family.
Write the fact family that includes 9, 3, and 6.
Write the fact family that includes 8, 7, and 1.
The sums are 6. One difference is 2. What is the third number of this fact family?
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Lesson 6
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Problem Solving
You can use objects to help solve problems.
Examples
Kyle has 3 yellow marbles, 4 red marbles, and 2 blue marbles. How many -marbles are there in all? Use ( ) to show two ways to group the addends.
Use objects to help you group.
Kyle has 9 marbles.
Solve
Use objects to help you solve these problems.
There are 6 green frogs, 11 spotted frogs, and 1 brown frog in a pond. How many frogs are there in all? Use ( ) to show two ways to group the addends.
Chapter 2 Test
Add. Write the sum.
Write the missing number.
Add. Be sure to add the numbers in ( ) first.
Use objects to help you solve this problem.
Karen has a sheet of stickers. There are 14 green stickers, 2 gold stickers, and 3 red stickers on the sheet. How many stickers are there in all? Use ( ) to show two ways to group the addends.
Subtract.
Subtract. Write the difference. Then write the missing addend in the box.
Complete each fact family.
Write the fact family that includes 17, 6, and 11.
Write the fact family that includes 19, 9, and 10.
