Why percentages matter for SSC CGL Tier 1
Every time you see a question about profit, discount, or interest, the answer hides behind a simple percentage trick. Spotting it can shave precious seconds off your paper.
💡 In Simple Words: A percentage is just a way to say “out of 100”. If you can turn a problem into “how many out of 100”, you can answer it with a quick mental step instead of long division.
What are percentage shortcuts?
A shortcut is a mental shortcut – a rule of thumb that lets you jump straight to the answer. For example, instead of calculating 15% of 80 by multiplying 0.15 × 80, you can think “10% of 80 is 8, half of that (5%) is 4, add them → 12”.
Core shortcuts you’ll see in SSC CGL
1. 10% × n = move the decimal one place left
Imagine sliding a decimal point left; that’s the same as taking a slice of a pizza that’s one‑tenth of the whole.
2. 5% × n = half of 10%
Take the 10% result and cut it in half. Easy, right?
3. 1% × n = move the decimal two places left
Two slides give you one‑hundredth of the number.
4. 20% = double 10%
Just double the 10% answer.
5. 25% = quarter of the number
Divide by 4 – think of sharing a pizza among four friends.
6. 50% = half the number
Split it straight down the middle.
7. 75% = 50% + 25%
Combine the half and the quarter.
Worked example 1: Discount problem
Question: A shirt is marked ₹ 1,200. It is offered at a 25% discount. What is the selling price?
Shortcut steps:
- Find 25% of 1,200 → quarter it: 1,200 ÷ 4 = 300.
- Discount amount = ₹ 300.
- Selling price = 1,200 – 300 = ₹ 900.
Using the shortcut you avoid any multiplication.
Worked example 2: Profit problem
Question: A trader buys a gadget for ₹ 560 and sells it for a 15% profit. What is the selling price?
Shortcut steps:
- 10% of 560 = 56.
- 5% of 560 = half of 56 = 28.
- 15% = 56 + 28 = 84.
- Selling price = 560 + 84 = ₹ 644.
Notice how the 10% + 5% trick saved you from a calculator.
Quick comparison table
| Percentage | Shortcut | How to think |
|---|---|---|
| 10% | Move decimal left 1 place | One slice of a 10‑slice pizza |
| 5% | Half of 10% | Half a slice |
| 1% | Move decimal left 2 places | One tiny crumb |
| 20% | Double 10% | Two slices |
| 25% | Quarter the number | One‑fourth of a pizza |
| 50% | Half the number | Split the pizza in half |
How to apply shortcuts in a flash
When you read a percentage question, pause for two seconds and ask:
- Is the percentage one of the easy numbers (5, 10, 25, 50, 75, 20)?
- Can I break it into a sum of those easy numbers?
- What base (the original amount) am I working with?
Answering these quickly tells you which shortcut to pull.
📝 Likely Exam Questions
- Find 30% of 250.
Answer: 10% = 25, triple it → 75. - A laptop costs ₹ 18,000. It is sold at a 12% profit. What is the selling price?
Answer: 10% = 1,800; 2% = 360; profit = 2,160; price = 20,160. - If a product is discounted by 40% and the discounted price is ₹ 3,600, what was the original price?
Answer: 40% = 4 × 10%; let original = x; 40% of x = 0.4x = 3,600 → x = 9,000. - Calculate 7.5% of 80.
Answer: 5% = 4; 2.5% = half of 5% = 2; total = 6; 7.5% = 6 + (0.5% = 0.4) ≈ 6.4 (or use 10%‑3% shortcut). - A shopkeeper marks an item at ₹ 2,500. He offers a 15% discount and then adds 5% sales tax on the discounted price. What does the buyer finally pay?
Answer: Discount 15% = 10% (250) + 5% (125) = 375; discounted price = 2,125. Tax 5% = half of 10% (212.5) = 106.25; final price ≈ 2,231.25.