Common Numerical Reasoning Mistakes
Numerical reasoning tests are designed to catch errors. Many candidates lose points due to mistakes that are easy to avoid with awareness and practice. Here are the most common ones and how to prevent them.
1. Wrong Base for Percentages
Mistake: Using the new value instead of the old value when calculating percentage change.
- Correct: ((New − Old) ÷ Old) × 100. The base is always the original (old) value.
- Example: 100 to 120 is a 20% increase. Wrong: (20 ÷ 120) × 100 = 16.7%. Right: (20 ÷ 100) × 100 = 20%.
2. Misreading "Increase By" vs "Increase To"
Mistake: Confusing "increased by 20%" (add 20% to original) with "increased to 120" (new value is 120).
- "Increased by" means add the percentage to the original.
- "Increased to" means the new value is given.
3. Unit Errors
Mistake: Ignoring units (e.g. £000 vs £, millions vs thousands). A value of 500 in a £000 column means £500,000.
- Always check column headers and units before calculating.
4. Rounding Too Early
Mistake: Rounding intermediate results and losing precision. In multi-step calculations, keep full precision until the final answer.
- Only round when the question asks for a rounded answer.
5. Rushing and Misreading
Mistake: Skimming the question and missing key details. Read the question twice before calculating.
- Underline key numbers and what is being asked.
How to Avoid These Mistakes
- Practise under timed conditions but prioritise accuracy.
- Double-check the formula and base for percentage questions.
- Verify units and column labels before calculating.
- Review practice tests to identify your own recurring errors.
Use numerical reasoning practice and the numerical reasoning test to build accuracy.
Frequently Asked Questions
What is the single most common mistake?
Using the wrong base for percentage change. Always use the original (old) value as the denominator.
How can I reduce careless errors?
Read the question twice, underline key numbers, and do a quick sanity check on your answer before submitting.
Should I guess if I'm unsure?
It depends on the test. Some penalise wrong answers; others do not. If there's no penalty, guessing may help. Check the instructions.