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Missing number problems

Missing number problems

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Explainer Video

Tutor: Alice

Summary

Missing number problems

​​In a nutshell

Expressions involving an unknown number are needed to solve missing number problems. Unknown numbers are usually represented by letters.


Example 1

x+10=12x + 10 = 12x+10=12

This is the same as asking: "what is added to 101010​ to get 121212​?"


The answer is x=2x=2x=2


Note: xxx is the letter commonly used for an unknown.



Method for solving

​​Procedure

1.
Write out an equation 
2.
Work out the value of the unknown
​
Example 2


Anna has £20£20£20​. She shares £5£5£5​ with her brother and uses £12£12£12​ to buy a new dress. how much money does she have left?

​

Write an expression:


5+12+x=205 + 12 + x = 205+12+x=20

Solve for xxx:

​x=3x= 3x=3​


Anna has £3‾\underline{£3}£3​​ remaining.

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Learn with Basics

Learn the basics with theory units and practise what you learned with exercise sets!
Length:
Two-step problems with addition and subtraction

Unit 1

Two-step problems with addition and subtraction

Adding and subtracting money

Unit 2

Adding and subtracting money

Jump Ahead

Score 80% to jump directly to the final unit.

Optional

Missing number problems

Unit 3

Missing number problems

Final Test

Test reviewing all units to claim a reward planet.

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FAQs - Frequently Asked Questions

How do I solve a missing number problem?

Use trial and error to try out possible solutions.

What do letters mean in an unknown number problem?

Unknown numbers are usually represented by letters.

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