Home

Maths

Algebra

Missing number problems

Select Lesson

Download

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

$x + 10 = 12$

This is the same as asking: "what is added to $10$ to get $12$?"

The answer is $x=2$

Note: $x$ is the letter commonly used for an unknown.

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

Write an expression:

$5 + 12 + x = 20$

Solve for $x$:

$x= 3$

Anna has $\underline{£3}$ remaining.

Optional

Create an account to complete the exercises

Use trial and error to try out possible solutions.

Unknown numbers are usually represented by letters.

Beta