1st Grade · 1.OA.A.2

Adding 3 numbers in 1st grade

Adding 3 numbers means finding the total of three amounts, such as 4 red apples, 6 green apples and 3 yellow apples. In 1st grade, your child solves word problems like this where the total is 20 or less. Your child uses objects, drawings and equations, and learns to add the easiest pair first.

What the standard says

The official Common Core wording, quoted exactly. The plain version follows.

1.OA.A.2 Solve 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.

What it means, in plain words

Adding three numbers works like adding two. Your child adds two of the numbers, then adds the third number to that total. A story might say that a child picks 5 strawberries, then 3, then 5 more. The equation is $5 + 3 + 5 = ?$ , where the question mark stands for the total.

The order of the numbers does not change the total, so your child can choose the easiest pair to add first. Two numbers that make 10, such as 7 and 3, are a good pair. Doubles, two of the same number like 5 and 5, are another. For $5 + 3 + 5$ , adding the two 5s first gives 10, and $10 + 3 = 13$ .

Adding 3 numbers in 1st grade keeps the total at 20 or less, so every step uses facts your child already knows from adding two numbers. A drawing helps too: three groups of circles, one group for each number in the story.

Your child should be able to:

Write an equation with three numbers for a story, such as $4 + 6 + 3 = ?$
Add three numbers with a total of 20 or less
Pick an easy pair to add first, such as two numbers that make 10
Show the story with objects or a drawing

Example

A child has 6 blue beads, 5 yellow beads and 4 red beads. How many beads is that in all?

Write the equation: $6 + 5 + 4 = ?$ .
6 and 4 make 10, so add them first.
Then add the 5: $10 + 5 = 15$ .
There are 15 beads in all.

Example

8 cars, 2 buses and 7 bikes go past the house. How many go past in all?

Write the equation: $8 + 2 + 7 = ?$ .
8 and 2 make 10, so add them first.
Then add the 7: $10 + 7 = 17$ .
17 cars, buses and bikes go past the house.

Where children usually get stuck

For 6 blue beads, 5 yellow beads and 4 red beads, your child adds 6 and 5 and writes 11 as the answer.
Most stories so far had two numbers, so the child stops after one addition.
What helps. Ask your child to point to each number in the story and put a tick under it once it has been added. A number without a tick is still waiting.
To add $9 + 1 + 6$ , your child counts out all 16 objects one by one from 1.
The child does not yet know that the numbers can be added in any order. So there is no reason to look for an easy pair.
What helps. Before adding, ask which two numbers make 10. Check with ten fingers, then count on from 10.
For $8 + 5 + 2$ , your child gets 13 after the first two numbers and then forgets whether the 2 has been added.
Keeping a total in mind while also tracking which numbers are used is a lot to hold at once for a 6-year-old.
What helps. Draw a curve joining the 8 and the 2, and write 10 under it. Then add the 5 to that 10 on paper: 15.

Try four practice questions

Real 1st grade questions from our question bank, easiest first. Answer them right here, check each one, and see a worked solution for any question.

1Warm-up
Aisha found 3 sunflowers, then 2 more, and then 4 more. How many sunflowers did Aisha find in all?
Which equation matches the story?
A
$\displaystyle 3 + {}$
$\displaystyle 2 - 4 = {}$
$\displaystyle ?$
B
$\displaystyle 3 + {}$
$\displaystyle 2 + {}$
$\displaystyle 4 = {}$
$\displaystyle ?$
C
$\displaystyle 3 + {}$
$\displaystyle 2 = {}$
$\displaystyle ?$
D
$\displaystyle 3 + {}$
$\displaystyle 2 + {}$
$\displaystyle ? = {}$
$\displaystyle 4$
Show the answer and how to solve it
The matching equation is $3 + 2 + 4 = ?$ because the story has three groups of sunflowers ( $3$ , $2$ , and $4$ ), and we need to find the total — so the three numbers are the addends and ? is the total.
1. 1Look at the story. Aisha found sunflowers three times: 3 sunflowers, then 2 more, and then 4 more. The picture shows the three groups joined with + signs.
2. 2The story asks for the total — how many sunflowers Aisha found in all. We don't know the total yet, so we use ? to stand for the unknown total.
3. 3To find the total of three groups, we add the three numbers and put ? after the equal sign for the total.
Common mistake. A common mistake is choosing $3 + 2 + ? = 4$ — this puts ? as one of the groups instead of the total. When a story tells you three groups and asks 'How many in all?', the unknown is always the total, not one of the groups.
The idea underneath. When a story tells you three groups and asks 'how many in all?', the matching equation has all three group numbers added together, with ? for the total.
2On level
Aisha saw 2 butterflies on Monday, 5 butterflies on Tuesday, and 4 butterflies on Wednesday. How many butterflies did Aisha see in all?
Drag tiles to build the addition equation that matches the story.
Tap or click a tile to drop it into the highlighted blank, or tap an empty blank first to choose a different one. Tap a filled blank to send its tile back.
+
+
= ?
2
5
4
3
6
7
Tap an item to place it in the next empty slot, or drag it to a specific slot. With a keyboard: select an item with Enter or Space, then select a slot to place it. Press Delete or Backspace on a slot to remove an item.
Show the answer and how to solve it
The equation is $2 + 5 + 4 = ?$ . The story gives three numbers — $2$ , $5$ , and $4$ — and we use $?$ for the total because we are not asked to compute it.
1. 1Find the three numbers in the story. Aisha saw $2$ butterflies, then $5$ butterflies, then $4$ butterflies. The picture also shows three groups with the same counts: $2$ , $5$ , and $4$ .
2. 2The three groups of butterflies join together. To find the total, add the three numbers.
3. 3We do not know the total yet, so we use $?$ to stand for the unknown total. The equation that matches the story is:
Common mistake. A common mistake is grabbing a number that isn't in the story, like $3$ (close to $2$ ) or $7$ (which is $2 + 5$ added together too soon). Use only the three numbers the story gives you: $2$ , $5$ , and $4$ .
The idea underneath. An equation can use a symbol like $?$ to stand for an unknown amount. The story tells you which numbers to add — you do not have to compute the total to write the equation.
3On level
Jamal saw 2 birds, then 5 more birds, then 3 more birds at the pond. Maria and Liam each wrote an addition equation to find how many birds Jamal saw in all.
$\displaystyle \begin{array}{l} \text{Maria: } 2 + 5 + 3 = ? \\ \text{Liam: } 3 + 2 + 5 = ? \end{array}$
Whose equation matches the story?
A
Only Maria's equation matches the story.
B
Only Liam's equation matches the story.
C
Both Maria's and Liam's equations match the story.
D
Neither Maria's nor Liam's equation matches the story.
Show the answer and how to solve it
Both Maria's and Liam's equations match the story. Both equations use the three numbers from the story — 2, 5, and 3 — as addends with ? for the unknown total. Adding the same numbers in any order gives the same total.
1. 1Look at the story. Jamal saw 2 birds, then 5 more, then 3 more. The three numbers in the story are 2, 5, and 3.
2. 2An equation that matches the story must use all three numbers as addends, with ? for the total.
3. 3Maria's equation uses 2, 5, and 3 as addends with ? for the total. Maria's equation matches the story.
4. 4Liam's equation uses 3, 2, and 5 as addends with ? for the total. He used the same three numbers as Maria, just in a different order. When you add numbers in any order, the total is the same. Liam's equation also matches the story.
5. 5Both Maria's and Liam's equations match the story.
Common mistake. A common mistake is thinking only one ordering of addends can match a story. Some students pick only Maria because her equation $2 + 5 + 3 =$ ? lists the numbers in story order. But Liam's equation $3 + 2 + 5 =$ ? uses the same three numbers — just in a different order — and addition gives the same total no matter the order. Both equations correctly match the story.
The idea underneath. When you add the same numbers in any order, the total is the same. So an addition equation can write the addends in any order and still correctly match a joining story.
4Stretch
Sam sees 3 frogs, 3 ducks, and 2 fish at the pond.
Drag the animals onto the pond to show what Sam sees.
Tap or click a picture, then tap the grid to place it. Tap a placed picture to remove it.
Show the answer and how to solve it
The pond should show 3 frogs, 3 ducks, and 2 fish — 8 animals altogether. Each number in the story matches exactly one group of animals.
1. 1Read the story carefully. Sam sees three groups of animals at the pond: 3 frogs, 3 ducks, and 2 fish. The numbers in the story tell you how many of each animal to put on the pond.
2. 2Drag 3 frogs onto the pond. Count as you drag each one: 1, 2, 3.
3. 3Drag 3 ducks onto the pond. Count as you drag: 1, 2, 3.
4. 4Drag 2 fish onto the pond. Count as you drag: 1, 2.
5. 5Check your work. The pond should have 3 frogs, 3 ducks, and 2 fish. Add to find the total: $3 + 3 + 2 = 8$ animals.
Common mistake. A common mistake is dragging the wrong count for one group — for example, dragging 2 ducks when the story says 3. Always match each number in the story to the right animal and count carefully as you drag each group.
The idea underneath. Each number in the story tells you exactly how many of that animal to put on the pond. Read the story one group at a time, drag that group, then check it before moving to the next group.