#11
Top 50 Mistake
Only doing the operation on one side
"The One-Sided Operation"
The Mistake in Action
Solve $3x = 18$
Wrong: $3x \div 3 = 18$ $x = 18$
Why It Happens
Students correctly identify that they need to divide by 3, but only apply it to the left side.
The Fix
Whatever you do to one side, you MUST do to the other side. The equation is like a balance scale — both sides must be treated equally.
$$3x = 18$$ $$\frac{3x}{3} = \frac{18}{3}$$ $$x = 6$$
Check: $3 \times 6 = 18$ ✓
Spot the Mistake
Can you identify where this student went wrong?
Solve $3x = 18$
$3x \div 3 = 18$
$x = 18$
Click on the line that contains the error.
Related Topics
Learn more about the underlying maths: