Why Percentage Shortcuts Matter in SSC CGL Tier 1
Every minute counts in a competitive exam. Knowing a few clever tricks can shave off precious seconds and keep you from simple mistakes.
A percentage is just a way of saying "out of 100". If you can turn a percentage problem into a quick mental math step, you’ll solve it faster than anyone else.
What is a Percentage, Really?
Think of a pizza cut into 100 tiny slices. If you eat 25 slices, you’ve eaten 25% of the pizza. In math, we write that as 25/100 or 0.25. The same idea works for money, marks, or any number.
Shortcut #1 – 10% is Easy as Moving the Decimal
Find 10% of a number by moving the decimal point one place left. Example: 10% of 480 is 48. Once you have 10%, getting 5% is just half of that, and 20% is double it.
Shortcut #2 – 1% = 10% ÷ 10
If you need 1%, first get 10% (move the decimal) then divide by 10. For 1% of 735, 10% is 73.5, so 1% is 7.35.
Shortcut #3 – 25% = Half of 50%
Half of a number is 50%. Half of that half again gives 25%. So 25% of 360 is half of 180, which is 90.
Shortcut #4 – 75% = 50% + 25%
Combine shortcuts: 50% is half, 25% is half of half. 75% of 200 = 100 (half) + 50 (quarter) = 150.
Shortcut #5 – % Increase/Decrease Using Difference
When something grows by 20%, add 20% of the original to the original. When it shrinks by 20%, subtract 20% of the original. Example: A salary rises from ₹40,000 to 20% more. 20% of 40,000 is 8,000, so new salary = 48,000.
Shortcut #6 – Quick % of a Number Using Multiples of 5
If the percentage is a multiple of 5, break it into 10% and 5% pieces. For 35% of 120: 10% = 12, 5% = 6, so 30% = 36, plus another 5% = 6, total = 42.
When to Use Which Shortcut?
- Numbers ending in 0 or 5 → use 10%/5% tricks.
- Small percentages (1‑3%) → use 10% ÷ 10 or 1% then multiply.
- Quarter or three‑quarter values → use 25% or 75% combos.
Quick Comparison: Traditional vs Shortcut
| Problem | Traditional Method | Shortcut Method |
|---|---|---|
| Find 18% of 250 | 250 × 0.18 = 45 (requires multiplication) | 10% = 25, 5% = 12.5, 2% = 5, 1% = 2.5 → 10%+5%+2%+1% = 25+12.5+5+2.5 = 45 |
Step‑by‑Step Flow for Any % Question
Follow these four moves and you’ll rarely get stuck.
📝 Likely Exam Questions
- Find 15% of 560.
Answer: 10% = 56, 5% = 28, total = 84. - A product costs ₹1,200. Its price is increased by 12%. What is the new price?
Answer: 10% = 120, 2% = 24, add to 1,200 → 1,344. - If a candidate’s marks go from 320 to 384, what is the percentage increase?
Answer: Increase = 64; 10% of 320 = 32, so 20% = 64 → 20% increase. - Calculate 7.5% of 80.
Answer: 5% = 4, 2.5% = 2, total = 6. - Discount of 25% on a bike priced at ₹80,000. What is the sale price?
Answer: 25% = quarter = 20,000; subtract → ₹60,000.