Addition Within 100

In this article, we will learn about Addition within 100. The learning objectives are:

1. Addition within 100 without renaming
2. Addition within 100 with renaming
3. Addition of three numbers

Topic recap: Addition within 20

Example 1:

How many chocolate tarts are there altogether?

__________ + __________ = __________

Answer:

14 tarts

Explanation: 

You can add by counting on.

$11 + 3 = 14$

There are 14 chocolate tarts altogether.

OR

You can also add by adding the ones first.

Step 1:

$11 = 10 + 1$

Step 2:

Add the ones first.

Step 3:

$\begin{align}​ 1 + 3 &= 4 \\ 10 + 4 &= 14 \\ 11 + 3 &= 14 \end{align}$

There are 14 chocolate tarts altogether.

Example 2:

$9 + 5 =$ __________

Answer:

14

Explanation:

You can also add by making 10 first.

Step 1: 

$9 = 4 + 5$

Step 2: 

Make 10 first.

Step 3:

$\begin{align}​ 5 + 5 &= 10 \\  10 + 4 &= 14\\    9 + 5 &= 14 \end{align}$

Example 3:

Add 15 and 3.

1. 17
2. 18
3. 19
4. 20

Answer:

(2) 18

Explanation: 

Split 15 into 10 and 5. 

Add 5 to 3. 

Add the total to 10.

$15 + 3 = 18$

Topic recap: Numbers within 100

Example 1:

Complete the number pattern.

$10 + 86 = ?$

Answer:

96

Explanation:

10 more than 86 is 96.

$10 + 86 = 96$

1. Addition within 100 without renaming 

Example 1:

Damien has 21 pencils. Claire has 5 pencils. How many pencils do they have altogether?

Answer:

26 pencils

Explanation:

Step 1:

$21 = 20 + 1$

Step 2: 

Add the ones first.

Step 3:

$\begin{align}​ 1 + 5 &= 6 \\ 20 + 6 &= 26 \\ 21 + 5 &= 26 \end{align}$

They have 26 pencils altogether.

So the answer is 26 pencils

OR

They have 26 pencils altogether.

Answer:

26 pencils

Question 1: 

Add 45 to 2.

1. 46
2. 47
3. 48
4. 49

Explanation:

Step 1:

$45 = 40 + 5$

Step 2:

Add the ones first.

Step 3:

$\begin{align}​ 2 + 5 &= 7 \\ 40 + 7 &= 47 \\ 45 + 2 &= 47 \end{align}$

Answer:

(2) 47

OR

$45 + 2 = 47$

Answer:

(2) 47

Example 2:

Jocelyn has 21 markers and Donnie has 40 markers. How many markers do they have altogether?

Explanation: 

Step 1: 

$21 = 20 + 1$

Step 2:

Add the tens first.

Step 3:

$\begin{align}​ 20 + 40 &= 60 \\ 60 + 1 &= 61 \\ 21 + 40 &= 61 \end{align}$

They have 61 markers altogether.

Answer:

61 markers

OR

They have 61 markers altogether.

Answer:

61 markers

Question 1: 

Add 33 to 50.

Explanation: 

Step 1:

$33 = 30 + 3$

Step 2:

Add the tens first.

Step 3:

$\begin{align}​ 30 + 50 &= 80 \\ 80 + 3 &= 83 \\  33 + 50 &= 83   \end{align}$

Answer:

83

OR

$33 + 50 = 83$

Answer: 

$83$

Example 3:

Jonathan has 44 crayons. May has 52 crayons. How many crayons do they have altogether?

Explanation:

They have 96 crayons altogether.

Answer:

96 crayons

Question 1: 

Add 31 and 24.

1. 35
2. 55
3. 57
4. 75

Explanation:

$31 + 24 = 55$

Answer:

(2) 55

Question 2: 

The sum of 74 and 23 is __________. 

1. 51
2. 57
3. 91
4. 97

Explanation:

Sum means  ‘$+$’.

$74 + 23 = 97$

Answer:

(4) 97

Question 3: 

4 tens $+$ 2 tens $=$ __________

1. 6
2. 16
3. 60
4. 66

Explanation:

4 tens $=$ 40

2 tens $=$ 20

$40 + 20 = 60$

Answer:

(3) 60

Question 4: 

Which of the following is the sum of 3 tens and 68?

Explanation: 

3 tens $=$ 30

$30 + 68 = 98$

Answer:

(3) 98

2. Addition within 100 with renaming

Example:

26 apples were sold in the morning. 9 apples were sold in the afternoon. How many apples were sold altogether?

Explanation:

$26 + 9 = 35$

35 apples were sold altogether.

Answer:

35 apples

Question 1: 

Solve the following:

$37 + 5 =$ __________

1. 12
2. 32
3. 42
4. 52                                                                       

Explanation:

$37 + 5 = 42$

Answer:

(3) 42

Question 2: 

Solve the following:

$45 + 19 =$ __________

1. 64
2. 65
3. 66
4. 67

Explanation:

$45 + 19 = 64$

Answer:

(1) 64

Question 3: 

The sum of 34 and 26 is __________.

1. 8
2. 50
3. 52
4. 60

Explanation:

$34 + 26 = 60$

Answer:

(4) 60

Question 4: 

Add 7 ones to 5 tens 8 ones. The answer is __________.

1. 55
2. 58
3. 65
4. 83

Explanation: 

7 ones $=$ 7

5 tens 8 ones $=$ 58

$58 + 7 = 65$

Answer:

(3) 65

Question 5: 

Which of the following has the greatest answer?

Explanation: 

Option 1:

$28 + 19 = 47$

Option 2:

$36 + 12 = 48$

Option 3:

$38 + 16 = 54$

Option 4:

$23 + 37 = 60$

The greatest answer is 60.

Answer:

(4) 60

Question 6: 

Which of the following numbers comes just after the sum of 29 and 55?

Explanation:

$29 + 55 = 84$

The number that comes just after 84 is 85. 

Answer:

(3) 85

3. Addition of three numbers

Example:

Elizabeth has 1 paper clip. Jackie has 4 paper clips and Joey has 5 paper clips. How many paper clips do the children have in all?

Explanation:

$\begin{align}​ 1 + 4 &= 5 \\ 5 + 5 &= 10 \end{align}$

The children have 10 paper clips in all.

Answer:

10 paper clips

Question 1: 

The sum of 7, 8 and 9 is __________.

1. 23
2. 24
3. 25
4. 34

Explanation: 

$\begin{align}​ 7 + 8 &= 15 \\ 15 + 9 &= 24 \end{align}$

Answer: 

(2) 24

Question 2: 

Which of the four options does not have the same value as the sum of 33 and 45?

Explanation:

$33 + 45 = 78$

We have to find an option that is not equal to 78. 

Option 1: 

78

Option 2: 

$\begin{align}​ 50 + 10 + 18 \\\\ 50 + 10 = 60 \\ 60 + 18 = 78 \end{align}$

Option 3: 

6 tens and 18 ones

   6 tens $=$ 60

18 ones $=$ 18

6 tens and 18 ones

$\begin{align}​ &= 60 + 18\\ &= 78 \end{align}$

Option 4: 

7 tens and 18 ones 

   7 tens $=$ 70

18 ones $=$ 18

7 tens and 18 ones

$\begin{align}​ &= 70 + 18 \\ &= 80 \end{align}$

Answer: 

(4) 7 tens 18 ones

Challenge yourself!

Question 1: 

Find the missing number in the box.

1. 16
2. 26
3. 36
4. 46

Explanation: 

$\begin{align}​ 24 + 12 &= 36 \\  ? + 10 &= 36 \\ 10 + 26 &= 36 \end{align}$

Answer: 

(2) 26

In this article, we have learnt:

• Addition within 100 without renaming
• Addition within 100 with renaming
• Addition of three numbers