Add within 100, including adding a two-digit number and a one-digit number, and adding a two-digit number and a multiple of 10, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used. Understand that in adding two-digit numbers, one adds tens and tens, ones and ones; and sometimes it is necessary to compose a ten.


Quarter 1
Quarter 2
Quarter 3
Quarter 4
Add within 100. Relate the strategy to a written method and explain the reasoning used. Including:

a. Adding a two-digit number and a one-digit number, within 100.

b. Adding a two-digit number and a multiple of 10, using:
concrete models drawings strategies based on place value properties of operations
the relationship between addition and subtraction

c. Understand that in adding two-digit numbers, it requires adding tens and tens, ones and ones; and sometimes it is necessary to compose a ten (without standard algorithm)
Add within 100. Relate the strategy to a written method and explain the reasoning used. Including:

a. Adding a two-digit number and a one-digit number, within 100.

b. Adding a two-digit number and a multiple of 10, using:
concrete models drawings strategies based on place value properties of operations
the relationship between addition and subtraction

c. Understand that in adding two-digit numbers, it requires adding tens and tens, ones and ones; and sometimes it is necessary to compose a ten (without standard algorithm)
Add within 100. Relate the strategy to a written method and explain the reasoning used. Including:

a. Adding a two-digit number and a one-digit number, within 100.

b. Adding a two-digit number and a multiple of 10, using:
concrete models drawings strategies based on place value, properties of operations, and the relationship between addition and subtraction

c. Understand that in adding two-digit numbers, it requires adding tens and tens, ones and ones; and sometimes it is necessary to compose a ten (without standard algorithm)
Add within 100. Relate the strategy to a written method and explain the reasoning used. Including:

a. Adding a two-digit number and a one-digit number, within 100.

b. Adding a two-digit number and a multiple of 10, using:
concrete models drawings strategies based on place value properties of operations
the relationship between addition and subtraction

c. Understand that in adding two-digit numbers, it requires adding tens and tens, ones and ones; and sometimes it is necessary to compose a ten (without standard algorithm)

Increasing Rigor

  • Anna scored 18 points in 3 games. What might her scores have been for each of the games?
  • Juan added three numbers to get 14. What could the three numbers be?
  • The sum of a two-digit number and a one digit number is 43? What might the numbers be?
  • Have students randomly pick a two-digit number from the hundred chart. Then roll a ten-sided die to find a digit to add to the number. What strategies are you using when you are adding? For example, in 48 + 7 = , students might say “I broke the 7 into 2 and 5 because I know 8 + 2 is 10 and so 48 and 2 is 50 and 5 more is 55?
  • Create some number sentences with the students and record three on the board. For example, 38 + 10 = 48, 24 + 30 = 54, 57 + 40 = 97. Ask "What patterns do you see?"
  • Use a 100 chart. Choose two numbers between 11 and 50 to add. Show how to use the chart to add the numbers without using pencil or paper.
  • Use six of the digits 1-9 (without repeating digits) to form 2 two-digit numbers with a two-digit sum that is true. (for example: 64 + 15 = 79) Can you think of another example?
  • Two two-digit numbers have a sum of 86. What could the addends be? What is another solution?
  • Start with the number 15, then have students reach into a bowl of tens and ones block and grab a handful of blocks to form a number. Add 15 to the other number. Compare your addition sentence to your neighbor’s addition sentence, how are they alike and how are they different?

About the Math

Students should work with invented strategies, number concepts, and operation concepts prior to learning the traditional algorithm. Working with open number lines is a good way to develop these concepts. Essential vocabulary for this standard includes: add, compose, decompose, and place value (online dictionary, HCPSS Vocabulary Cards).

Rich Tasks for Multiple Means of Engagement, Expression, and Representation (UDL)

Little Ten-Frame Addition and Subtraction (Van de Walle, K-3, p 149). Provide a set of little ten-frame cards to each pair of students. One student makes a two-digit number with multiple ten-frames and ones (ex- 54 can be made with five full ten-frames and four ones). The second student may either select a one digit number or multiple full ten frames to show a two-digit multiple of ten. When both have their numbers ready, they place it out so both can see. Then they try to be the first to tell the total. For subtraction, again one student makes a two digit number with multiple ten-frames and ones. The second child writes on paper a one digit number or a multiple of 10 to be subtracted from the model number. Students should be encouraged to share strategies to see how fast they can get at solving

Students should initially be exposed to the computational strategy of direct modeling (counting by ones and the use of base ten models), then invented or flexible strategies, and finally the traditional algorithm. This will enable them to move from the concrete, then to the semi concrete, and finally to the abstract. Students may use a variety of methods to add, for example:

Journal Prompts:

  • Using 0-9 digit cards, turn over two cards to make a two-digit number. Roll your die and add the number shown. Record and repeat.
  • Represent 17 with base 10 blocks. Add another set of 10 and record the new number. Continue adding one more set of 10 until you reach 97. What pattern do you notice?
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Strategies for Addition:
Addition Strategies
This file outlines different strategies for adding whole numbers.
Add On Tens, Then Add Ones
You can decompose one of the numbers
33 + 26
33 and 20 is 53.
Then 6 more is 59.
Move Some to Make Tens
To add 33 + 26,students may add 33 + 7 = 40
Then think 19 + 40 = 59.
Add Tens, Add Ones, Combine
Students may split the tens and ones apart.
33 + 26 can be thought of as 30 + 20 + 3 + 6
30 + 20 = 50
3 + 6 = 9
50 + 9 -= 59

Print Resources

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Brain Compatible Activities
for Mathematics K-1
(36-39, 57-59)

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Mental Math in the
Primary Grades
(66-76)

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Number Talks

Web Resources:

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Games and Centers
Lessons
Student Resources
Video Segments
Printables
What Number is...?
Adding 2 Digit and One Digit Numbers
Adding a Multiple of 10
The Game of Tens and Ones
Addition Split
Subtraction SplitLucky 6
Sums of 90
Funny Numbers
Place Value
Sam's Base Ten Blocks
10 more
Lesson Seeds
Using Place Value to Teach Addition and Subtraction
Add and Subtract
Sugar, Sugar!
Adding Big Numbers with Butterflies
Use Models to Add




Online Tools
How Many Cows?
100 Splat Squares

Practice Sheet / Homework
Computation with Sticks and Dots
(Erin Reisberg, Centennial Lane)
Partial Sums
Adding Making 10's
Adding Making 20's
Models Partial Sums (1-20)
Model Partial Partial Sums (1-20)
Breaking Into Tens and Ones

Illustrative Mathematics
Saving Money







Children's Literature

Click on the books for additional activities.
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Fair Bear Share



Questions/Comments:

Contact John SanGiovanni at jsangiovanni@hcpss.org.


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Howard County Public Schools Office of Elementary Mathematics Curricular Projects has licensed this product under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.