Finding the Unknown Number (in Addition) — Let's Practice!
 Finding the Unknown Number in Addition – Introduction
 What Is Finding the Unknown Number in Addition?
 Finding the Unknown Number in Addition – Example
 Finding the Unknown Number in Addition – Guided Practice
 Finding the Unknown Number in Addition – Application
 Finding the Unknown Number in Addition – Summary
 Finding the Unknown Number in Addition – Frequently Asked Questions
Basics on the topic Finding the Unknown Number (in Addition) — Let's Practice!
Finding the Unknown Number in Addition – Introduction
Get a piece of paper and a pencil ready because today we're going to practise finding the unknown number in addition. It’s a cool trick that helps you figure out missing parts in maths 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 practise this with some fun problems!
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 

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 practising finding the unknown number in addition to become a maths whiz! Check out more fun maths problems and activities on our website.
Finding the Unknown Number in Addition – Frequently Asked Questions
Finding the Unknown Number (in Addition) — Let's Practice! exercise

How many toys did Imani buy?
HintsRemember, an equation looks like this: part + part = whole.
To work out the missing part, think about how many more you need to add to 9 to reach 12.
Look at this example: Imani has 10 sweets. They get more and now they have 14 sweets. How many did they get?
The equation is: the part we know + the part we don't know = the whole we know.
So
10 + ? = 14
Count on from 10 to reach 14. 10, 11, 12, 13, 14. We counted on 4 more, so 10 + 4 = 14.
SolutionImani started with 9 toys and ended up with 12 in total, so the equation is 9 + ? = 12.
To find the missing part, count on from 9 to 12. 9, 10, 11, 12. We counted on 3 so this is the missing part.
9 + 3 = 12
The equation 3 + 9 = 12 would also have been correct.

Which numbers are missing?
HintsRemember, 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. We counted on 7, so the missing part is 7.
7 + 7 = 14
Solution7 + 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)

What is the missing part?
HintsCount 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
Solution5 + 6 = 11
3 + 7 = 10
9 + 4 = 13
To find the missing numbers, we started at the part we knew and counted up until we reached the whole.

How many flowers did Imani plant?
HintsRemember, 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.
SolutionImani planted 5 flowers.
The equation is: 8 + 5 = 13.
We count up from one part (8) to the whole (13) to find the missing part.
8, 9, 10, 11, 12, 13. The missing number is 5.

How many more nails did Mr. Squeaks find?
HintsMr. Squeaks started with 5 nails and finished with 10. Count up from 5 to 10 to find the missing part.
5, 6, 7, 8, 9, 10. How many numbers did we count up?
SolutionMr. Squeaks found 5 nails in the box.
Count on from 5 to 10: 5, 6, 7, 8, 9, 10. We counted 5 numbers, so 5 is the missing part.
5 + 5 = 10.

The vegetable patch.
HintsStart with the tomato plants.
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).
Repeat these steps for the bean plants.
SolutionTomato plants
 4 + ? = 13
 The missing part is 9.
 Count on from 4 to 13. 4, 5, 6, 7, 8, 9, 10, 11, 12, 13. We counted 9 numbers, so 9 is the missing part.
 4 + 9 = 13
 7 + ? = 11
 The missing part is 4.
 Count on from 7 to 11. 7, 8, 9, 10, 11. We counted on 4 numbers, so 4 is the missing part.
 7 + 4 = 11