5 Algebra Mistakes That Cost Students Easy Marks

Most lost marks in algebra aren't from hard concepts, they're from small, repeatable slips. Here are the five we see most often, and how to stop making them.

1. Dropping a negative sign

The classic. When you expand a bracket with a negative in front, every term flips:

$$-(2x - 5) = -2x + 5$$

Writing -2x - 5 here is the single most common error in the whole subject.

2. Distributing incorrectly

Multiplication must hit both terms inside the bracket:

$$3(x + 4) = 3x + 12 \quad\text{not}\quad 3x + 4$$

3. Cancelling across a sum

You can only cancel factors, never individual terms in a sum. This is wrong:

$$\frac{x + 2}{2} \neq x$$

The 2 on the bottom divides the whole numerator, not just the 2 on top.

4. Mishandling powers

When multiplying powers you add the indices; you don't multiply them:

$$x^3 \cdot x^2 = x^{5} \quad\text{not}\quad x^{6}$$

5. Forgetting the second solution

A quadratic usually has two roots. After factorising, don't stop at the first:

$$x^2 - 5x + 6 = 0 \;\Rightarrow\; (x-2)(x-3)=0 \;\Rightarrow\; x = 2 \ \text{or}\ x = 3$$

How to stop making them

• Slow down on sign changes, they cause more lost marks than anything else.
• Check by substituting your answer back into the original equation.
• Practise deliberately on the specific slip you make most.

The fastest way to fix a recurring mistake is to do lots of targeted questions on it. On ILMINO your mistakes feed straight into your mastery scores, so the platform keeps serving you the exact type of question you keep getting wrong until it sticks. Practise your weak topics and watch these slips disappear.