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🔬 Science ⏱ 3 min read

How to Solve Equations and Find Missing Numbers

Learn how to solve equations by finding the missing number using simple balancing tricks.

Age 9–12
KS3 Ages 11-14
Reading level: |

What is an Equation?

An equation is like a puzzle where you need to find a missing number. It's a statement that says two things are equal. For example, x + 5 = 12 means "some number plus 5 equals 12"—and your job is to work out what that number is.

The letter x (or any letter) stands for the missing number we need to find. This missing number is called the unknown.

Think of it like a seesaw at the playground. When both sides are balanced, they weigh the same. An equation works the same way—both sides of the equals sign must stay balanced.

The Golden Rule: Keep Both Sides Equal

The most important rule in solving equations is this: whatever you do to one side of the equation, you must do to the other side. This keeps everything balanced.

If we have x + 5 = 12, we need to get x on its own. To do this, we remove the 5 from the left side. But if we take away 5 from the left, we must also take away 5 from the right to keep it balanced:

x + 5 − 5 = 12 − 5

This simplifies to x = 7.

Think of it like sharing sweets between two friends. If one person loses 5 sweets, the other person must lose 5 sweets too, so it stays fair.

Steps to Solve Any Equation

Step 1: Identify what you need to get rid of on the side with the x.

Step 2: Do the opposite operation. If you're adding, subtract. If you're subtracting, add. If you're multiplying, divide. If you're dividing, multiply.

Step 3: Do that same operation to both sides of the equation.

Step 4: Simplify until x stands alone.

Step 5: Check your answer by putting the number back into the original equation.

Think of it like unwrapping a present. If something is added around your answer, you peel it away. If something is multiplied around it, you divide it away.

A Quick Example

Let's solve 3x = 15.

Here, x is being multiplied by 3. To undo multiplication, we divide both sides by 3:

3x ÷ 3 = 15 ÷ 3

This gives us x = 5.

To check: 3 × 5 = 15 ✓ Correct!

Once you practise these steps, solving equations becomes a satisfying puzzle where you're in control of finding the answer.

Test yourself 🧠

This quiz is calibrated for KS3.