Core ConceptRead this first — the foundation of the topic
Basic Percentage is the foundation of all percentage problems in SSC CGL. It measures parts per hundred. The word 'percent' comes from Latin 'per centum' meaning 'by hundred'. Understanding this concept is crucial as it appears in 2-3 questions in every SSC CGL paper. Core Concept: Percentage is a way to express a fraction with denominator 100. When you say 25%, it means 25 out of 100 parts. Think of it as cutting a pie into 100 equal slices and taking some of them.
Key RulesCore rules you must know cold
First, percentage is always calculated on a base value. Second, 100% means the complete quantity. Third, percentages can exceed 100% when the part is larger than the whole. Fourth, percentage change and percentage of a number are different concepts.
Formula BlockMemorise — at least one formula appears in every paper
• Percentage = (Part/Whole) × 100
• Part = (Percentage/100) × Whole
• Whole = (Part × 100)/Percentage
• Percentage to Fraction: x% = x/100
• Percentage to Decimal: x% = x/100 = 0.0x
Exam PatternsWhat examiners ask — read before attempting PYQs
Powerful Shortcuts for Quick Calculation
Shortcut 1 - Common Percentage Conversions:
• 50% = 1/2, 25% = 1/4, 20% = 1/5, 10% = 1/10
• 33.33% = 1/3, 66.67% = 2/3, 12.5% = 1/8, 16.67% = 1/6
Memorize these to solve faster without calculations
Shortcut 2 - Quick Mental Math Trick
• For 15% of any number: Take 10% + 5%
• For 35% of any number: Take 30% + 5%
• Break complex percentages into easier chunks
Worked ExampleSolve this step-by-step before moving on
1
Step 1
Convert percentage to decimal: 24% = 24/100 = 0.24
Add: 170 + 34 = 204
Answer: 24% of 850 = 204
Worked Example 2: What percentage is 156 of 240?
1
Step 1
Use formula: Percentage = (Part/Whole) × 100
2
Step 2
Substitute values: (156/240) × 100
3
Step 3
Simplify fraction: 156/240 = 13/20 (dividing by 12)
4
Step 4
Convert to decimal: 13/20 = 0.65
5
Step 5
Multiply by 100: 0.65 × 100 = 65%
Answer: 156 is 65% of 240
Shortcut 3 - The Unitary Method for Percentages:
If x% = y, then 1% = y/x, and 100% = (y × 100)/x
This eliminates complex calculations in competitive exams.
Exam TrapsCommon mistakes students make — avoid these
- The #1 Trap: Students confuse 'percentage of' with 'percentage more than'. For example, if A is 20% of B, it does NOT mean A is 20% more than B. '20% of B' means A = 0.20 × B. But '20% more than B' means A = B + 0.20 × B = 1.20 × B.
This confusion costs precious marks in exams.
Another frequent error is forgetting to convert percentage back to the required form. Always check if the answer needs to be in percentage, decimal, or fraction format.
Key Points to Remember
Percentage means parts per hundred, always calculated on a base value
A shopkeeper marks the price of an item at ₹500. He offers a discount of 12% on the marked price. What is the selling price of the item?
Practice 2medium
A shopkeeper marks up the price of an item by 40% above its cost price. He then offers a discount of 20% on the marked price. If the cost price of the item is ₹500, what is his profit percentage?
Practice 3hard
A shopkeeper marks up the cost price of an item by 60%. He then offers a discount of 25% on the marked price. If the cost price is ₹800, what is his profit percentage?
60-Second Revision — Basic Percentage
Remember: Percentage = (Part/Whole) × 100 for all basic problems
Formula: Part = (Percentage/100) × Whole for finding quantities
Trap: 'x% of y' ≠ 'x% more than y' - completely different meanings
Shortcut: Use fraction conversions (25% = 1/4) for faster calculations
Quick check: 50% should always give exactly half the original number