Percentage shortcuts that save time in numerical reasoning tests
You do not need to be fast at maths to ace percentage questions. You need three shortcuts (build from 10%, reverse via decimals, sanity-check the result) and a week of daily drills. That turns arithmetic into recognition.
- Build awkward percentages from 10%, 5% and 1% instead of calculating from scratch.
- For percentage change, divide by the original value, not the new value.
- For reverse percentages, turn the percent into a decimal and divide.
- Always estimate before choosing the answer; it catches most slips.
Percentages become fast only when you drill them against a clock. Start numerical practice
Percentages dominate numerical reasoning because they are easy to ask and hard to do fast under stress. Your goal is not to become a mental maths wizard. Your goal is to memorise a few repeatable shortcuts that turn arithmetic into recognition. For the full numerical method, start with the numerical reasoning guide; for broad drill coverage, use the worked practice questions.
The shortcut table
| Target | Fast method | Example |
|---|---|---|
| 10% | Move the decimal one place. | 10% of 420 = 42 |
| 5% | Half of 10%. | 5% of 420 = 21 |
| 1% | Divide by 100. | 1% of 420 = 4.2 |
| 15% | 10% + 5%. | 15% of 420 = 63 |
| 25% | Divide by 4. | 25% of 420 = 105 |
| 12% | 10% + 1% + 1%. | 12% of 420 = 50.4 |
Shortcut set A: build from 10%
- 10% = move the decimal one place (£420 → £42).
- 5% = half of 10%.
- 1% = 10% ÷ 10.
Then compose: 15% = 10% + 5%, 12% = 10% + 2%, 35% = 10% × 3 + 5%. You almost never need to compute a percentage from scratch.
Shortcut set B: reverse percentages
If £84 is 70% of X, then X = 84 / 0.70 = 120. The fast habit is to convert the percent to a decimal immediately. Do not divide by 70 — divide by 0.70. That single change removes half the arithmetic errors people make on reverse percentages.
Original = 126 / 0.84 = 150. Sanity check: 84% is close to 80%, and 126 / 0.8 = 157.5, so ~150 passes the smell test.
Shortcut set C: percentage change
Percentage change is where candidates lose the most easy marks. The formula is always:
Percentage change = change / original value x 100
If sales rise from 80 to 100, the change is 20 and the original value is 80. The increase is 20 / 80 x 100 = 25%. Dividing by the new value gives 20%, which is a common distractor.
Shortcut set D: sanity checks
Before picking an option, ask:
- “If it is an increase, is the result bigger than the original?”
- “If it is 20%, is it close to one-fifth?”
- “If it is a reduction, did I subtract from the correct base?”
Worked example: discount then increase
After the discount: 200 x 0.80 = 160. After the increase: 160 x 1.10 = 176.
The trap is adding -20% and +10% to get -10%. Percentages apply to the current base, so the final price is £176, not £180.
A 7-day drill that actually works
Set a timer for 2 minutes and do 20 calculations:
- 10%, 5%, 1%, 15%, 25% of random numbers between 40 and 800.
- Repeat daily for 7 days.
You will notice real speed improvements by day 4 — not because your brain is faster, but because recognition has replaced computation.
How to review percentage mistakes
Tag each miss as one of three types: wrong base, arithmetic slip, or misunderstood wording. Wrong-base errors mean you need more percentage-change drills. Arithmetic slips mean you need estimation before answer selection. Wording errors mean you should slow down on phrases like “of the original”, “after the increase” and “as a percentage of total”. If your percentage errors mostly happen inside tables and charts, move next to data interpretation.
Source notes
forge checks percentage-test guidance against official SHL numerical examples, including SHL’s numerical reasoning example questions and practice test pages. Provider timing and calculator rules still vary.
Drill percentages on forge
Timed percentage drills and mixed numerical sets, with one-line diagnoses on every wrong answer.
See what forge offersFrequently asked questions
What percentage shortcuts matter most for numerical reasoning?+
Start with 10%, 5%, 1%, 25%, reverse percentages and percentage change from the original value. Those cover most timed test percentage questions.
Should I use a calculator for percentages?+
Use one if the real test allows it, but still learn the shortcuts. Estimation and base checks help you catch calculator input errors.
Why do I get percentage change questions wrong?+
The most common error is dividing by the new value instead of the original value. Percentage change uses change divided by the starting value.
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