#14
Top 50 Mistake
Errors when collecting x terms
"The Collection Confusion"
The Mistake in Action
Solve $5x + 2 = 2x + 14$
Wrong: $5x + 2x = 14 + 2$ $7x = 16$
Why It Happens
Students try to get all x terms on one side but add instead of subtract (or vice versa).
The Fix
Be systematic: choose one side for x terms and one side for number terms.
Correct method: $$5x + 2 = 2x + 14$$
Subtract $2x$ from both sides (collecting x on the left): $$3x + 2 = 14$$
Subtract 2 from both sides: $$3x = 12$$
Divide by 3: $$x = 4$$
Check: LHS = $5(4) + 2 = 22$, RHS = $2(4) + 14 = 22$ ✓
Spot the Mistake
Can you identify where this student went wrong?
Solve $5x + 2 = 2x + 14$
$5x + 2x = 14 + 2$
$7x = 16$
Click on the line that contains the error.
Related Topics
Learn more about the underlying maths: