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Add a Two-Digit Number and a Single-Digit Number Mentally

This is a complete lesson for 2nd grade math where children learn to add a 2-digit number and a single-digit number mentally, without crossing to the next ten, such as 35 + 4 or 61 + 5. They add "within" the same ten. The lesson contains both instruction and plenty of exercises, and even a 'bonus' puzzle problem in the end.



  +  
25 + 3 = 28

Add  5 + 3  first.
The 2 tens do not change.

+  
12 + 7 = 19

Add  2 + 7  first.
The ten does not change.

+  
34 + 4 = 38

Add  4 + 4  first.
The 3 tens do not change.

1. Write an addition sentence for each picture.

a.   +

_______ + _______ = ______

b.   +

_______ + _______ = ______

c.    +

_______ + _______ = ______

d.    +

_______ + _______ = ______

2. Add. Compare the problems. The top problem helps you solve the bottom one!

a.  5  +  2  = _____

   35  +  2  = _____

b.  4  +  5  = _____

   64  +  5  = _____

c.  3  +  6  = _____

   93  +  6  = _____

3. Add. For each problem, think about a “helping” problem with numbers less than 10.

a.  52 + 7 = _____

   2   +   7   = _____

b33 + 1 = _____

____ + ____ = _____

c.  11 + 5 = _____

_____ + ____ = _____



4. The numbers are written in boxes! Add ones in their own column.
    Copy the tens number down below.

a.  35 + 3

    tens ones
3 5
+  ↓ 3
3 8

b.  12 + 6

    tens ones
1 2
+  ↓ 6
   

c.  57 + 1

    tens ones
5 7
+  ↓ 1
   

d.  64 + 3

    tens ones
6 4
+  ↓ 3
   

5. Now you write the numbers in the boxes. Add ones in their own column.

a.  26 + 3

    tens ones
   
+  ↓  
   

b.  72 + 4

    tens ones
   
+  ↓  
   

c.  65 + 4

    tens ones
   
+  ↓  
   

d.  81 + 4

    tens ones
   
+  ↓  
   

6. Add. Compare the problems.

a.

6 + 2 = ______

16 + 2 = ______

36 + 2 = ______

b.

4 + 3 = ______

24 + 3 = ______

34 + 3 = ______

c.

 5 + 4 = ______

45 + 4 = ______

65 + 4 = ______

d.

11 + 7 = ______

61 + 7 = ______

41 + 7 = ______

7. Add many numbers.

a.

20 + 5 + 2 = ______

44 + 2 + 2 = ______

b.

93 + 1 + 5 = ______

83 + 4 + 3 = ______

c.

 100 + 5 + 4 = ______

52 + 4 + 2 = ______



 Remember how to break
 a number into its
 TENS and ONES?
      
23  =   20  + 3
    tens   ones
        

  

47  =   40  + 7
    tens   ones

8. Break the numbers into tens and ones or do it the other way around.

a.

18  =     10   +    8     

25  = _____ + _____

55  = _____ + _____

b.

32  = _____ + _____

95  = _____ + _____

______  =  40   +   9

c.

_______ = 60  +  6

_______ = 9  +  80

_______ = 8  +  70

9. Compare. Write < > , or = .

a.  24 + 3 24 + 5
  
b83 + 5 85 + 3
c. 17 + 2 19 + 2
  
d36 + 4 46 + 4
e.  58 8 + 51
  
f.  66 5 + 61

 

    is a number we don't know—a mystery number! Your task
   is to compare without knowing the mystery number! 
   For example, which is more, + 2  or  + 7?
 
Write < or  > in the boxes. Note: t
here is one comparison you cannot do without knowing the mystery number. Can you find it?

+ 5 

     + 4      – 5      – 4       – 5       

 

   

+ 2

  + 7

– 5

  – 6 +   + 20


This lesson is taken from my book Math Mammoth Add & Subtract 2B. The lesson addresses the following Common Core standards for 2nd grade: 2.OA.1 and 2.NBT.5.

Math Mammoth Add & Subtract 2-B

A self-teaching worktext for 2nd grade that covers mental addition and subtraction with two-digit numbers, and regrouping in addition and subtraction (carrying & borrowing).

Download ($5.65). Also available as a printed copy.

=> Learn more and see the free samples!

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