# Unknown Addend in Addition Problems - first grade

This is a complete lesson with instruction and exercises for initial teaching on the UNKNOWN or MISSING ADDEND concept in first grade math. Children solve simple addition equations with single-digit numbers where one addend is missing or unknown.

Something is missing from the addition.
The TOTAL is not missing. The total is 5.

How many are in the second group? That's what is missing!

There should be a total of 5 dots. Draw 4 in the second die face.

 5 + 1   + ______

There should be a total of 4 dots. The second die face has two.
There are none in the first die face, so you need to draw them.

Read: “2 plus what number makes 4?”
or,  “2 and how many more makes 4?”
or,  “What number and 2 makes 4?”

 4 + ______  +  2

1. Draw more dots for the addition. Write the missing number. The total is on top.

 3 + a.    1     +  _____
 3 + b.    2     +  _____
 5 + c.  _____ +   4
 5 + d.    3     +  _____
 5 + e.  _____ +   2
 4 + f.  _____ +   3
 5 + g.    5     +  _____
 4 + h.  _____ +   1
 4 + i.  _____ +   2

 + 3    +  _____ =   5
The TOTAL is now written after
the equal sign “ = ”.
The answer is 3  +   2   =  5

 + _____  +    3 =   4
See the TOTAL written after
the equal sign “ = ”.
The answer is    1   +  3 =  4

2. Draw more dots to show the missing number. Write the missing number.

 a. + 2  + _____ =  4
 b. + 1  + _____ = 1
 c. + _____ + 1 =  5
 d. + 3  + _____ =  5
 e. + _____ + 1 =  4
 f. + 2  + _____ =  3
 g. + 5  + _____ =  5
 h. + _____ + 1 =  3
 i. + 2  + _____ =  5
 j. + 1 + _____ =  5
 k. + _____ + 2 =  2
 l. + 3  + _____ =  4

3. Draw more dots in the empty box for the missing number. Read the problems aloud:
“2 plus how many makes 4?”

 +

a.   2  + ______ = 4

 +

b.   4  + ______ = 4

 +

c. ______ + 3 = 4

 +

d.   2  + ______ = 5

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e. ______ + 1 = 3

 +

f. ______ + 4 = 5

There are no dots in either die face.

The first die face is missing the dots. The second die face is supposed to have none, since there is a zero below it.

Draw 4 dots in the first die face, because  4  + 0 =  4 .

 + ______ +    0 =   4

4. Draw dots in the boxes for the missing numbers. Notice that some boxes are supposed
to have zero dots.

 +

a.   0  + ______ =  4

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b.   2  + ______ =  2

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c. ______ + 0  =  3

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d.   3  + ______ =  3

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e. ______ + 0  =  2

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f.   0  + ______ =  1

5. Draw dots to illustrate each addition problem. Find what number is missing.

 +

a.  4  + ______ =  5

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b.  1  + ______ =  2

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c. ______ + 3  =  5

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d.  3  + ______ =  4

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e.  2  + ______ =  3

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f. ______ + 2  =  4

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g.  1  + ______ =  5

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h. ______ + 1  =  4

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i.  3  + ______ =  3

6. Solve. Now, the missing number goes inside the shape. You can draw dots to help you.
Remember, the number after the “ = ” sign is the total.

 a.  2 +  = 5 b.  + 2 = 4 c.  + 1 = 3 d.  + 3 = 3 e.  3 + = 5 f.  0 +  = 2 g.  3 +  = 4 h.  + 2 = 4 i.  + 1 = 5

7. Practice “normal” addition.

 a.   1 + 1 = ______     2 + 1 = ______ b.   4 + 0 = ______     3 + 1 = ______ c.   1 + 4 = ______    2 + 2 = ______ d.   2 + 3 = ______     1 + 4 = ______ e.   0 + 5 = ______     1 + 2 = ______ f.   3 + 2 = ______     4 + 1 = ______

8. Find the missing number. The marbles illustrate the total. Notice the patterns!

 a. 0 +  ______  = 3 1 +  ______  = 3 2 +  ______  = 33 +  ______  = 3 b. 0 +  ______  = 4 1 +  ______  = 4 2 +  ______  = 4 3 +  ______  = 4 4 +  ______  = 4 c. 0 +  ______  = 5 1 +  ______  = 5 2 +  ______  = 53 +  ______  = 54 +  ______  = 55 +  ______  = 5

This lesson is taken from Maria Miller's book Math Mammoth Addition 1, and posted at www.HomeschoolMath.net with permission from the author. Copyright © Maria Miller. The lesson addresses the following Common Core standard for 1st grade: 1.OA.8.

#### Math Mammoth Addition 1

A self-teaching worktext for 1st grade that covers addition concept, missing addend problems, and practice of addition facts within the context of fact families (providing structure for the facts learning).

Download (\$3.95). Also available as a printed copy.

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