1.OA.1: Solve Word Problems Within 20
Also written as 1.OA.A.1 and CCSS.MATH.CONTENT.1.OA.A.1 · Cluster: Represent and solve problems involving addition and subtraction.
The Official Wording
Use 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.
Common Core State Standards, Grade 1, Operations & Algebraic Thinking · Read it at the source · Checked October 14, 2026
What 1.OA.1 Means in Plain English
First graders solve stories within 20 about joining, taking away, putting together, breaking apart and comparing, and the missing number can sit anywhere. “Maya had some stickers, got 5 more, and now has 12” hides the start: ? + 5 = 12.
Start-unknown and compare stories are the hard ones, because the action in the story points the wrong way. Objects, a quick drawing and a box for the unknown carry the load. In 2nd grade the numbers reach 100 and some stories take two steps (2.OA.1).
1.OA.1 I Can Statements
- I can solve a story problem within 20 with objects or a drawing.
- I can find the missing number at the start, middle or end.
- I can write an equation with a box for the unknown.
1.OA.1 Worked Example
A start-unknown story, the hardest of the joining types, worked with a drawing first and the equation last.
Maya had some stickers. Her teacher gave her 5 more. Now she has 12 stickers. How many stickers did Maya have at the start?
- Find what we do not know. We know what she got and what she has now. The start is missing.? + 5 = 12
- Draw 12 circles for all the stickers she has now, then circle the 5 the teacher gave her.12 circles, 5 of them circled
- The circles that are not circled are the stickers she had at the start. Count them.1, 2, 3, 4, 5, 6, 7
- Put the answer in the box and read the equation back.7 + 5 = 12
Check it: Act it out forward: 7 stickers and 5 more is 12, the number the story ends with.
Common Mistakes with 1.OA.1
Adding the two numbers in the story
? + 5 = 12 answered with 17
Try this: Ask the student to act the story out from the start, then check whether 17 stickers and 5 more could ever make 12.
Adding in a compare story
“Ben has 9 cars and Ana has 4. How many more does Ben have?” answered with 13
Try this: Line up the two rows of cars one to one and count the cars in Ben’s row that have no partner.
Circling the wrong number
Writes 7 + 5 = 12 and circles 12 as the answer
Try this: Underline the question before solving, and after solving put the answer back into a story sentence: Maya had 7 stickers.
Where 1.OA.1 Fits
Practice 1.OA.1
Quick Check
- There are 8 children on the slide and 6 on the swings. How many children are playing?
- Leo had 15 crayons. He gave some to Sara, and now he has 9. How many crayons did he give Sara?
- Ava read 11 books. Sam read 4 fewer books than Ava. How many books did Sam read?