Add and subtract within 100

Here you will learn how to add and subtract within 100, including adding and subtracting two-digit numbers using base ten blocks, number lines, the break apart strategy or mental math, and the standard algorithm.

Students will first learn about adding and subtracting within 100 as part of number and operations in base ten in 2 nd grade.

What is adding and subtracting within 100?

Adding and subtracting within \bf{100} is when you add or subtract two-digit numbers using place value strategies and models, such as base ten blocks, or the standard algorithm.

Students will first begin adding within 100 in first grade including adding a two-digit number and a one-digit number and adding a two-digit number and a multiple of 10, using the strategies shown below.

However, according to the CCSS, they do not begin adding and subtracting 2 -digit numbers as the examples show until second grade.

To add within 100 using base ten blocks:

  • Draw the base ten blocks to represent the tens and ones. For addition, combine the tens and combine the ones. Regroup if necessary, then count the total tens and total ones. See the examples below.

Add and subtract within 100 1 US

To subtract within 100 using base ten blocks:

  • Draw the larger number, then cross off the number of tens and ones in the smaller number. Count the remaining tens and ones.
    Note that if there are not enough ones to cross off, you’ll need to exchange 1 ten for 10 ones first. See the examples below.

Add and subtract within 100 2 US

To add and subtract within 100 using a number line:

  • Draw a number line and use it to visually add or subtract. Move forward on the number line for addition and backward for subtraction.

Add and subtract within 100 3 US

To add and subtract within 100 using mental math or the break apart strategy:

  • Split each number into tens and ones. Add or subtract the tens. Add or subtract the ones together. Then combine the remaining tens and ones.

Add and subtract within 100 4 US

To add within 100 using the standard algorithm:

  • Stack the numbers vertically, placing the larger addend on top; be sure to line up the place values correctly. Start by adding the numbers in the smallest place value (the ones place). If the sum is greater than 9, carry over the tens place to the next column. Continue adding each column, regrouping as needed, until all columns are added.

Add and subtract within 100 5 US

To subtract within 100 using the standard algorithm:

  • Stack the numbers vertically, placing the larger addend on top; be sure to line up the place values correctly. Start by subtracting the numbers in the smallest place value (the ones place). If the digit on top is smaller than the one below, borrow from the next higher place value. Continue subtracting each column, borrowing as needed, until all columns are subtracted.

Add and subtract within 100 6 US

What is adding and subtracting within 100?

What is adding and subtracting within 100?

Common Core State Standards

How does this relate to 2 nd grade math?

  • Grade 2: Number and Operations in Base Ten (2.NBT.B.5)
    Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.

  • Grade 2: Operations and Algebraic Thinking (2.OA.A.1)
    Use addition and subtraction within 100 to solve one- and two-step word problems involving situations of adding to, taking from, putting together, taking apart, and comparing, with unknowns in all positions, e.g., by using drawings and equations with a symbol for the unknown number to represent the problem.

[FREE] Addition and Subtraction Worksheet (Grade 2, 3, 4 and 7)

[FREE] Addition and Subtraction Worksheet (Grade 2, 3, 4 and 7)

[FREE] Addition and Subtraction Worksheet (Grade 2, 3, 4 and 7)

Use this quiz to check your grade 2, 3, 4 and 7 students’ understanding of addition and subtraction. 15+ questions with answers covering a range of 2nd, 3rd, 4th and 7th grade addition and subtraction topics to identify areas of strength and support!

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[FREE] Addition and Subtraction Worksheet (Grade 2, 3, 4 and 7)

[FREE] Addition and Subtraction Worksheet (Grade 2, 3, 4 and 7)

[FREE] Addition and Subtraction Worksheet (Grade 2, 3, 4 and 7)

Use this quiz to check your grade 2, 3, 4 and 7 students’ understanding of addition and subtraction. 15+ questions with answers covering a range of 2nd, 3rd, 4th and 7th grade addition and subtraction topics to identify areas of strength and support!

DOWNLOAD FREE

How to add and subtract within 100

In order to add and subtract within 100\text{:}

  1. Choose a strategy (Base ten, Number line, Break apart / Mental math, Standard algorithm).
  2. Solve.

Add and subtract within 100 examples

Example 1: two-digit addition (base ten blocks)

34 + 16 = \; ?

  1. Choose a strategy (Base ten, Number line, Break apart / Mental math, Standard algorithm).

You can use base ten blocks to add. Set up using base ten blocks to represent each number.

Add and subtract within 100 7 US

2Solve.

Combine the tens and the ones, then counting the total. For this problem, you’ll need to regroup 10 ones into 1 ten before counting the totals.

Add and subtract within 100 8 US

Example 2: two-digit subtraction (base ten blocks)

49-24=\; ?

Choose a strategy (Base ten, Number line, Break apart / Mental math, Standard algorithm).

Solve.

Example 3: two-digit addition (number line)

43 + 19 = \; ?

Choose a strategy (Base ten, Number line, Break apart / Mental math, Standard algorithm).

Solve.

Example 4: two-digit subtraction (number line)

76-28=\; ?

Choose a strategy (Base ten, Number line, Break apart / Mental math, Standard algorithm).

Solve.

Example 5: two-digit addition (break apart strategy)

68 + 31 = \; ?

Choose a strategy (Base ten, Number line, Break apart / Mental math, Standard algorithm).

Solve.

Example 6: two-digit subtraction (break apart strategy)

52-27=\; ?

Choose a strategy (Base ten, Number line, Break apart / Mental math, Standard algorithm).

Solve.

Example 7: addition word problem (standard algorithm)

A farmer placed 38 red apples and 26 green apples into a basket. How many apples are in the basket altogether?

Choose a strategy (Base ten, Number line, Break apart / Mental math, Standard algorithm).

Solve.

Example 8: subtraction word problem (standard algorithm)

Jack had 74 marbles. He gave 18 marbles to his friend. How many marbles does Jack have now?

Choose a strategy (Base ten, Number line, Break apart / Mental math, Standard algorithm).

Solve.

Teaching tips for adding and subtracting within 100

  • Create printable worksheets with mixed addition and subtraction problems within 100 that include an answer key for students to self-assess their work and check for errors. (Start with just addition worksheets and subtraction worksheets before creating mixed worksheets.)

  • Make room for math games and flashcards in lesson plans to allow students to continuously practice addition and subtraction facts. This will help prevent calculation errors when adding and subtracting within 100 and boost 1 st grade math skills.

  • Use models such as number bonds to help students determine what operation to use when solving word problems.

  • Give students completed examples of adding and subtracting using the standard algorithm with missing numbers and ask them to fill in the blanks. This will help them build a stronger understanding of the standard algorithm and prepare them for 3 rd grade math and beyond.

  • Encourage students to use number bonds to determine if a word problem is an addition problem or a subtraction problem.

Easy mistakes to make

  • Forgetting to regroup or exchange
    Students may forget to regroup or exchange when the sum or difference exceeds 9 in one place value.

  • Misaligning digits in the standard algorithm
    When using the standard algorithm, digits must be stacked vertically, aligning the digits that are in the same place value. Not doing so will lead to calculation errors.

Practice add and subtract within 100 questions

1. Solve 35 + 27.

52
GCSE Quiz False

62
GCSE Quiz True

8
GCSE Quiz False

53
GCSE Quiz False

Using base ten blocks:

 

Model the tens and ones in each number.

 

Add and subtract within 100 19 US

 

Combine the tens and ones.

 

Add and subtract within 100 20 US

 

You can create one new group of ten from 10 ones.

 

Add and subtract within 100 21 US

 

This leaves 6 tens and 2 ones, which is 62.

 

Therefore, 35+27=62.

2. Solve 94-58.

36
GCSE Quiz True

44
GCSE Quiz False

46
GCSE Quiz False

152
GCSE Quiz False

You can use a number line to count back from 94 to 58.

 

Add and subtract within 100 22 US

3. Solve 72+18=\; ?

54
GCSE Quiz False

86
GCSE Quiz False

80
GCSE Quiz False

90
GCSE Quiz True

You can use the break apart strategy to solve.

 

First, break each number into tens and ones.

 

72 = 70 + 2

 

18 = 10 + 8

 

Add the tens from each number.

 

70 + 10 = 80

 

Add the ones from each number.

 

2 + 8 = 10

 

Combine the tens and ones.

 

80 + 10 = 90

 

Therefore, 72 + 18 = 90

4. Solve 65-32=\; ?

97
GCSE Quiz False

32
GCSE Quiz False

33
GCSE Quiz True

23
GCSE Quiz False

You can use the break apart strategy to solve.

 

First, break each number into tens and ones.

 

65=60+5

 

32=30+2

 

Subtract the tens.

 

60-30=30

 

Subtract the ones.

 

5-2=3

 

Combine the tens and ones.

 

30 + 3 = 33

 

Therefore, 65-32=33

5. Solve 48+37=\; ?

11
GCSE Quiz False

75
GCSE Quiz False

86
GCSE Quiz False

85
GCSE Quiz True

You can use the standard algorithm to add the numbers.

 

Add and subtract within 100 23 US

6. Solve 98-27 =\; ?

71
GCSE Quiz True

61
GCSE Quiz False

125
GCSE Quiz False

75
GCSE Quiz False

You can use the standard algorithm to subtract the numbers.

 

Add and subtract within 100 24 US

Add and subtract within 100 FAQs

How do you add and subtract within \bf{100} in second grade math?

You can add and subtract within 100 ( 2 digit addition and subtraction) using a variety of strategies based on place value, such as base ten blocks, number lines, break apart strategies, and the standard algorithm.

How can you use place value understanding to add and subtract within \bf{100}?

You can use place value understanding to add and subtract within 100 by breaking numbers into tens and ones, making it easier to perform regrouping or exchanging (carrying over or borrowing) when necessary.

What are strategies you can use to add and subtract within \bf{100}?

You can use base ten blocks, number lines, the break apart strategy or mental math, and the standard algorithm to add and subtract within 100.

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