Addition and Subtraction Stories Within 20

Quick answer

Story problems come in a few kinds: some add to a group, some take from it, some put two parts together or take a whole apart, and some compare two groups. The missing number can be at the end, in the middle or at the start. A drawing or a number sentence with a box for the missing number shows which numbers are parts and which is the whole, and that tells whether to add or subtract.

What you'll learn

Solve add-to, take-from, put-together, take-apart and compare stories within 20
Write a number sentence with a box for the missing number
Solve stories that add three numbers

Kinds of stories

Every add or subtract story fits one of these kinds.

Kind	Story
Add to	Mia has $8$ shells. She finds $5$ more.
Take from	There are $12$ apples. We eat $3$ .
Put together	There are $6$ red cars and $7$ blue cars.
Take apart	There are $10$ kids. $4$ are boys and the rest are girls.
Compare	Ana has $9$ stickers. Ben has $6$ .

Each story has a number we do not know yet. We can write it as a box: $8 + \square = 13$ . The box is the missing number.

The missing number can be anywhere

In some stories, the missing number is at the end:

8 + 5 = \square

In some, it is in the middle: $7 + \square = 12$ . And in some, it is at the start: $\square - 4 = 9$ .

The story tells you where it goes. Write the numbers in the order the story happens.

Why finding the whole tells you what to do

Every story has a whole and parts. The parts go together to make the whole.

If you know both parts, add to find the whole.
If you know the whole and one part, take away to find the other part.

That is all it takes. Do not hunt for clue words. Look for the whole.

Worked examples

Common mistakes

Practice problems

Sam has $9$ grapes. He gets $6$ more. How many grapes does he have now?

Answer

$15$

Full solution

Both numbers are parts, so add: $9 + 6 = \square$ . $9 + 1 = 10$ , and $5$ more is $15$ .
There are $14$ ducks in a pond. $5$ swim away. How many are left?

Answer

$9$

Full solution

The whole is $14$ . Take away the $5$ : $14 - 5 = 9$ .
Kim had $6$ pencils. Her dad gave her some more. Now she has $11$ . How many did her dad give her?

Answer

$5$

Full solution

$6 + \square = 11$ . Count on from $6$ : $7$ , $8$ , $9$ , $10$ , $11$ . That is $5$ .
There are $15$ kids. $8$ are in the gym and the rest are outside. How many are outside?

Answer

$7$

Full solution

The whole is $15$ and one part is $8$ . Take away: $15 - 8 = 7$ .
Some cookies were on a plate. Dad ate $3$ . Now there are $8$ . How many were there at first?

Answer

$11$

Full solution

$\square - 3 = 8$ . The start is the whole. Add the parts: $8 + 3 = 11$ .
Max has $12$ blocks. Nia has $7$ . How many fewer blocks does Nia have?

Answer

$5$

Full solution

Find the gap between $12$ and $7$ : $12 - 7 = 5$ . Nia has $5$ fewer.
A box has $5$ red crayons, $2$ blue ones and $5$ yellow ones. How many crayons in all?

Answer

$12$

Full solution

$5 + 5 = 10$ . Then $10 + 2 = 12$ .
Tia has $8$ stamps. That is $4$ more than Jon has. How many stamps does Jon have?

Answer

$4$

Full solution

Tia has more, so Jon has fewer. Take away: $8 - 4 = 4$ .
Fill in the box: $\square + 9 = 16$ .

Answer

$7$

Full solution

The whole is $16$ and one part is $9$ . $16 - 9 = 7$ . Check: $7 + 9 = 16$ .
“Some kids were on the bus. $6$ got off. Now $7$ are on it. How many were on it at first?” Zoe writes $7 - 6 = 1$ . What went wrong?

Hint

Is the number at first bigger or smaller than $7$ ?

Answer

The start is missing, so it is the whole. $7 + 6 = 13$ kids.

Full solution

The story is $\square - 6 = 7$ . Before $6$ got off, there were more kids on the bus, not fewer.

The whole is the $7$ who stayed plus the $6$ who got off: $7 + 6 = 13$ .

Frequently asked questions

What kinds of word problems are in first grade?

Stories that add to a group, take from a group, put two parts together, take a whole apart, and compare two groups, all within 20.

What does the box in 7 + □ = 12 mean?

It stands for the missing number. Here it asks what number goes with 7 to make 12. The answer is 5.

How do I know whether to add or subtract?

Find the whole and the parts. If you need the whole, add the parts. If you need a part, take the other part away from the whole.

Does the word 'more' always mean add?

No. 'Ana has 3 more than Ben' can call for subtracting to find Ben's number. Think about the story, not one word.

How do I add three numbers?

Add two of them, then add the third. It helps to pick two that make 10 first: 4 + 3 + 6 is 4 + 6 = 10, then 10 + 3 = 13.

What to learn next

Standards alignment

This lesson covers the following Common Core State Standards for Mathematics.

CCSS.MATH.CONTENT.1.OA.A.1Operations and Algebraic ThinkingUse addition and subtraction within 20 to solve word problems involving situations of adding to, taking from, putting together, taking apart, and comparing, with unknowns in all positions, e.g., by using objects, drawings, and equations with a symbol for the unknown number to represent the problem.
CCSS.MATH.CONTENT.1.OA.A.2Operations and Algebraic ThinkingSolve word problems that call for addition of three whole numbers whose sum is less than or equal to 20, e.g., by using objects, drawings, and equations with a symbol for the unknown number to represent the problem.

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