Why Percentage Shortcuts Matter for SSC CGL Tier 1
Imagine solving a 20‑question paper in half the time because you can zap through percentage problems like a calculator. That’s the edge these shortcuts give you.
💡 In Simple Words: A percentage is just a part of 100. If you can turn any percentage question into a quick “divide by 100” or “multiply by a friendly number” step, you’ll finish faster and make fewer mistakes.
Core Idea: Turn Percentages into Easy Multiplications
Most percentage questions boil down to two actions: find the base (the whole) and apply the percent as a fraction of 100. When you remember a few handy fractions—like 10% = 1/10, 5% = 1/20, 25% = 1/4—you can replace long division with mental math.
Shortcut 1 – The 10% & 5% Trick
Finding 10% of a number is as simple as moving the decimal one place left. Half of that gives you 5%.
- Example: 10% of 240 = 24. So 5% = 12.
- Now 15% = 10% + 5% = 24 + 12 = 36.
Use this whenever the required percent is a multiple of 5.
Shortcut 2 – The 1% Rule (Divide by 100)
When you need an odd percent like 7% or 23%, first find 1% by shifting the decimal two places left, then multiply.
- Example: 1% of 850 = 8.5. So 7% = 8.5 × 7 = 59.5.
This works fast if you’re comfortable with simple multiplication.
Shortcut 3 – Percentage Increase / Decrease
Increase: New value = Original × (1 + %/100). Decrease: New value = Original × (1 – %/100). Think of it as adding or subtracting the percent part from the whole.
- Example: 20% increase on 150 → 150 × 1.20 = 180.
- Example: 12% decrease on 250 → 250 × 0.88 = 220.
Multiplying by 1.xx or 0.xx is quicker than finding the extra amount separately.
Shortcut 4 – Friendly Fractions (25%, 20%, 50%)
These percentages line up with easy fractions:
- 25% = 1/4 (just halve twice).
- 20% = 1/5 (divide by 5).
- 50% = 1/2 (half).
Example: 25% of 96 → 96 ÷ 4 = 24.
Quick Reference Table
| Percent | Easy Fraction / Trick | How to Compute Quickly |
|---|---|---|
| 5% | 1/20 | Half of 10% |
| 10% | 1/10 | Move decimal left one place |
| 12.5% | 1/8 | Half of 25% |
| 20% | 1/5 | Divide by 5 |
| 25% | 1/4 | Divide by 4 |
| 33.33% | 1/3 | Third of the number |
| 50% | 1/2 | Half |
Step‑by‑Step Flow for Any Percentage Question
Putting It All Together – Practice Makes Perfect
Let’s stitch a few problems together so the shortcuts feel natural.
- Find 18% of 275. 10% = 27.5, 5% = 13.75, 1% = 2.75. 18% = 10% + 5% + 2% + 1% → 27.5 + 13.75 + 5.5 + 2.75 = 49.5.
- A price rises from ₹1,200 to ₹1,452. What’s the percent increase? Increase = 252. Base = 1,200. % = (252/1,200)×100 = 21%.
- What is 30% of 84? 10% = 8.4, so 30% = 8.4×3 = 25.2.
Notice how each step avoids heavy division.
📝 Likely Exam Questions
- What is 15% of 640?
Answer: 10% = 64, 5% = 32, total = 96. - A product costing ₹750 gets a 12% discount. Find the sale price.
Answer: 12% of 750 = (10% + 2%) = 75 + 15 = 90. Sale price = 750 – 90 = 660. - If a population grows from 2,500 to 2,975, what is the percent increase?
Answer: Increase = 475. % = (475/2,500)×100 = 19%. - Find 33.33% of 300 using a shortcut.
Answer: 33.33% ≈ 1/3, so 300 ÷ 3 = 100. - A salary is reduced by 8% and becomes ₹46,200. What was the original salary?
Answer: New = 92% of original → Original = 46,200 ÷ 0.92 = 50,217.39 (≈ ₹50,217).