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Change Missing Number Problems into Algebra (1)

In this worksheet, students express missing number problems algebraically.

'Change Missing Number Problems into Algebra (1)' worksheet

Key stage:  KS 2

Curriculum topic:   Algebra

Curriculum subtopic:   Express Problems Algebraically

Difficulty level:  

Worksheet Overview

In this activity, we'll be learning how to change missing number problems into algebra.


So first... what is algebra?


Confused Child


We use algebra when we don't know the exact numbers in a calculation, and to do this we use letters to stand for numbers that we are trying to find.



Algebra is like a language with its own rules!  Let's look at some of the rules we need to know.


1) a stands for a number (we can use any letter)

2) a + 2 is 2 more than the number.

3) a - 7 is 7 less than the number.

4) 5a is 5 times the number (we don't use the × sign in algebra because it looks like the letter x).

5) a/4 or ¼ a is a quarter of the number or the number divided by 4. (N.B. We don't use the ÷ sign in algebra.)



Let's now use our algebra knowledge to work out the following problem:

 I think of a number.

1)  I double it and 2) take away 5.

3) I get 21.


Write this using algebra.

Use n for the number I think of.



n is the number I think of.

1) Double it to get 2n (remember this means 2 times n)

2) Take away 5 to get 2n - 5

3) This equals 21, so we write:

2n - 5 = 21



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