# Finding the Unknown Number (in Addition) — Let's Practice!

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Finding the Unknown Number (in Addition) — Let's Practice!
CCSS.MATH.CONTENT.1.OA.A.1

## Finding the Unknown Number in Addition – Introduction

Get a piece of paper and a pencil ready because today we're going to practice finding the unknown number in addition. It’s a cool trick that helps you figure out missing parts in math problems. Ready to begin? Let's go!

## What Is Finding the Unknown Number in Addition?

Finding the unknown number in addition means using parts and the whole to find the missing number in an addition problem.

For example, if you know how many items you started with and how many you ended with, you can find out how many were added. Let’s practice this with some fun problems!

What does finding the unknown number in addition mean?
How do you find the unknown number?
Why do we use this method?

## Finding the Unknown Number in Addition – Example

Let's solve a problem to find the unknown number:

Problem

If Emma started with 7 bits of wood for her new project and ended up with 12, how many bits did she add?

Solution

Follow these simple steps to find the solution.

Step Explanation Pictorial representation
Write the equation 7 + ? = 12
Count up from the part (7) to the whole (12) Count: 8, 9, 10, 11, 12
Find how many numbers you counted 5

So, the missing number is 5! Emma added 5 bits of wood.

## Finding the Unknown Number in Addition – Guided Practice

Let's try another problem together.

Problem

John started with 8 screws and finished with 11. How many screws did he add?

So, the missing number is 3! John added 3 screws.

## Finding the Unknown Number in Addition – Application

Now, try solving this problem on your own:

Problem If Sarah has a pile of 10 seeds and ends with a pile of 16 seeds, how many seeds did she add?

So, the missing number is 6! Sarah added 6 seeds.

### Finding the Unknown Number in Addition – Examples

To be truly fluent in finding the unknown number in addition, have a look at some more examples and complete them by following the steps.

Problem Equation Count Up Solution
9 + ? = 15 9 + ? = 15 10, 11, 12, 13, 14, 15 6
6 + ? = 13 6 + ? = 13 7, 8, 9, 10, 11, 12, 13 7
4 + ? = 10 4 + ? = 10 5, 6, 7, 8, 9, 10 6
3 + ? = 8 3 + ? = 8 4, 5, 6, 7, 8 5

## Finding the Unknown Number in Addition – Summary

Key Learnings from this Text:

• Finding the unknown number in addition helps us solve addition problems by using parts and the whole.
• Write an equation with the parts you know.
• Count up from the known part to the whole to find the missing number.

Keep practicing finding the unknown number in addition to become a math whiz! Check out more fun math problems and activities on our website.

What is finding the unknown number in addition?
How do you use this method?
Why is it helpful to find the unknown number?
Can you give an example?
What should you remember when finding the unknown number?
What is the "whole" in an addition problem?
How do you write an equation for finding the unknown number?
What do you do after writing the equation?
Is this method only used in addition?
Where can I practice more problems like this?

### TranscriptFinding the Unknown Number (in Addition) — Let's Practice!

Razzi says get a piece of paper and pencil ready (...) Because today we're going to practice... Finding the unknown number (in addition). It's time to begin! Remember, you can use parts, whole, and addition to help find the missing number. If Mr. Squeaks started with seven bits of wood for his new project, and ended up with twelve, how many bits did he add? Remember to write an equation, and fill in the parts that you know. Then, count up from part one until you reach the whole. How many numbers did you count? Did you also count five? So, the missing number is five! Let's tackle the next problem! Mr. Squeaks now has started building using screws. If he started with eight screws and finished with eleven, how many screws did he add? Remember to write an equation, and fill in the parts that you know. Then, count up from part one until you reach the whole. How many numbers did you count? Did you also count three ? So, the missing number is three! Let's tackle the next problem! If Mr. Squeaks has a pile of ten seeds and ends with a pile of sixteen seeds, how many seeds did he add? Remember to write an equation, and fill in the parts that you know. Then, count up from part one until you reach the whole. How many numbers did you count? Did you also count six ? The missing number is six! Razzi had so much fun practicing with you today! See you next time!

## Finding the Unknown Number (in Addition) — Let's Practice! exercise

Would you like to apply the knowledge you’ve learned? You can review and practice it with the tasks for the video Finding the Unknown Number (in Addition) — Let's Practice!.
• ### Show the correct equation.

Hints

Remember, an equation looks like this: part + part = whole

Look at this example. Imani has 10 candies. He gets more, and now he has 14 candies. How many did he get?

The equation is: the part we know + the part we don't know = the whole we know.

10 + ? = 14

Solution

The equation we would write is 4 + ? = 13. We know Imani had 4 toys. Then, they added more and end with 13. The whole is 13, and one part is 4: 4 + ? = 13.

To solve, Imani counts up from 4 (5, 6, 7, 8, 9, 10, 11, 12, 13) to find that they added 9 toys from the store.

4 + 9 = 13

• ### Select the appropriate numbers to complete the equations.

Hints

Remember, to find the part we don't know, we count up from the part we do know until we reach the whole.

Look at this example. 7 + ? = 14.

We start at the part we know (7) and count up to the whole (14).

7, 8, 9, 10, 11, 12, 13, 14. The missing part is 7.

Solution

7 + 3 = 10 (7, 8, 9, 10)

3 + 6 = 9 (3, 4, 5, 6, 7, 8, 9)

8 + 7 = 15 (8, 9, 10, 11, 12, 13, 14, 15)

• ### Fill in the missing part.

Hints

Count up from the part you know until you reach the whole.

Look at this example: 8 + ? = 14.

We start at 8, and count up until we reach 14.

8, 9, 10, 11, 12, 13, 14. The missing part is 6.

8 + 6 = 14

Solution

5 + 6 = 11

3 + 7 = 10

9 + 4 = 13

To find the missing numbers, we started at the part and counted up until we reached the whole.

• ### Create the equation and solve.

Hints

Remember, to create an equation, use the numbers you know. We know Mr. Squeaks planted 8 flowers. What else do we know?

Look at the story. What is the whole? How many flowers did they plant together?

An equation looks like this: part + part = whole

To find the missing part, start at the part we know and count up to reach the whole.

Solution

Imani planted 5 flowers.

The equation is: 8 + 5 = 13.

We count up from one part (8) to the whole (13) to solve for the missing part.

8, 9, 10, 11, 12, 13. The missing number is 5.

• ### Count up to find the missing part.

Hints

Mr. Squeaks started with 6 toys and finished with 10. Count up from 6 to find the missing part.

Part + part = whole

Solution

Imani gave Mr. Squeaks 4 toys today!

Mr. Squeaks already had 6 toys, and Imani gave him more. Now he has 10 toys. The equation is: 6 + ? = 10.

To solve, start at 6, and count up until 10. 6, 7, 8, 9, 10. The missing part is 4.

• ### Finish the equation and solve.

Hints

Remember, to create an equation, use the numbers you know. We know Imani planted 4 tomatoes. What else do we know?

Look at the story. What is the whole? How many tomatoes did they plant together?

An equation looks like this: part + part = whole

To find the missing part, start at the part we know (4) and count up to reach the whole (13).

Solution

Mr. Squeaks planted 9 tomato plants!

The equation is: 4 + 9 = 13.

We count up from one part (4) to the whole (13) to find the missing part.

4, 5, 6, 7, 8, 9, 10, 11, 12, 13. The missing number is 9*