Study Material — 1 PYQs (2018–2018) · Concept Notes · Shortcuts
SSC CHSL Percentage Change is a frequently tested subtopic — 1 previous year questions from 2018–2018 papers are included below with concept notes, key rules and shortcut tricks.
1 questions from actual SSC CHSL papers · all shown free · click option to reveal solution
Exam Q 12018Previous Year Pattern
The price of a commodity increased by 25% in January and then decreased by 20% in February. What is the net percentage change in the price at the end of February compared to the original price?
Concept Notes
Percentage Change— Rules & Concept
Core ConceptRead this first — the foundation of the topic
Percentage change is the difference between the original value and the new value, expressed as a percentage of the original value. This concept appears in almost every SSC CGL paper and forms the backbone of profit-loss, simple interest, and data interpretation questions. Core Concept: When any quantity increases or decreases, we calculate the percentage change to measure the rate of change. For example, if your salary increases from Rs 20,000 to Rs 25,000, the percentage increase is 25%.
Formula BlockMemorise — at least one formula appears in every paper
Block:
• Percentage Increase = [(New Value - Original Value) / Original Value] × 100
• Percentage Decrease = [(Original Value - New Value) / Original Value] × 100
• New Value after x% increase = Original Value × (100 + x)/100
• New Value after x% decrease = Original Value × (100 - x)/100
• Successive percentage changes: If a value changes by a% then b%, final change = [a + b + (ab/100)]%
Exam PatternsWhat examiners ask — read before attempting PYQs
SSC loves asking percentage change in population growth, salary hikes, price fluctuations, and successive discounts. Questions often involve finding original values when final values and percentage changes are given.
ShortcutsUse these to save 30–60 seconds per question
1
Two successive increases of x% = (x + x + x²/100)% total increase
2
One increase of x% followed by decrease of x% = (x²/100)% net decrease
3
25% increase means multiply by 1.25
4
20% decrease means multiply by 0.8
5
12.5% increase means multiply by 9/8
Worked ExampleSolve this step-by-step before moving on
1
Step 1
Identify original value = 50,000, new value = 65,000
2
Step 2
Find increase = 65,000 - 50,000 = 15,000
3
Step 3
Apply formula = (15,000/50,000) × 100 = 30%
Answer: 30% increase
Worked Example 2:
A number is first increased by 20% and then decreased by 15%. Find the overall percentage change.
1
Step 1
Let original number = 100 (always take 100 for easier calculation)
2
Step 2
After 20% increase = 100 × 1.2 = 120
3
Step 3
After 15% decrease = 120 × 0.85 = 102
4
Step 4
Overall change = 102 - 100 = 2
5
Step 5
Percentage change = 2% increase
Alternative: Using formula = 20 + (-15) + (20×(-15)/100) = 20 - 15 - 3 = 2% increase
Shortcut Trick #3: Percentage to fraction conversions:
• 12.5% = 1/8, 16.67% = 1/6, 33.33% = 1/3, 66.67% = 2/3
• These help in quick mental calculations during exams.
Exam TrapsCommon mistakes students make — avoid these
#1: Students often confuse which value to use as base. Remember: percentage change is always calculated on the ORIGINAL value, not the new value. If price changes from Rs 100 to Rs 120, the base is Rs 100, not Rs 120.
Many students calculate (20/120) × 100 instead of (20/100) × 100, leading to wrong answers.
Exam Strategy: Practice reverse calculations where you find original values from final values and percentage changes. SSC frequently tests this concept in tricky word problems involving multiple successive changes.
Key Points to Remember
Percentage change = [(New Value - Original Value) / Original Value] × 100
Always use original value as denominator, never the new value
Successive changes formula: a + b + (ab/100) for changes of a% and b%
A shopkeeper increases the price of a shirt by 25%. If the original price was ₹400, what is the new price?
Practice 2easy
A shopkeeper reduced the price of a shirt from ₹800 to ₹600. What is the percentage decrease in price?
Practice 3easy
The population of a town decreases by 20% in one year. If the population at the end of the year is 64,000, what was the population at the beginning of the year?
Practice 4easy
The price of petrol decreased by 10% and then increased by 10%. If the original price was ₹100 per litre, what is the final price?
Practice 5easy
A company's revenue increased from ₹50 lakhs to ₹60 lakhs. What is the percentage increase in revenue?
Practice 6easy
A student's marks increased from 60 to 75. What is the percentage increase in marks?
Practice 7easy
The price of a book increased from ₹200 to ₹250. What is the percentage increase in price?
Practice 8easy
The population of a town was 50,000 in 2020. If it increased by 20% in 2021, what was the population in 2021?
Practice 9medium
The value of a car depreciates by 15% in the first year and then by 10% in the second year. If the original value was ₹5,00,000, what is the value of the car after two years?
Practice 10medium
A shopkeeper buys goods at ₹800 per unit. He marks up the price by 50% and then offers a discount of 30% on the marked price. What is the percentage profit or loss on the cost price?
Practice 11medium
The price of a commodity increases by 25% in the first year and then decreases by 20% in the second year. What is the net percentage change in price over the two years?
Practice 12medium
A shopkeeper buys an item for ₹400. He marks it up by 50% and then offers a discount of 30% on the marked price. What is his profit or loss percentage?
Practice 13medium
A retailer sells an item at a 40% profit. If the selling price is ₹840, what was the cost price?
Practice 14medium
A student's marks increased from 60 to 75. Later, due to re-evaluation, the marks decreased from 75 to 72. What is the net percentage change in marks from the original score of 60?
Practice 15hard
A salary is increased by 15%, then decreased by 8%, then increased by 10%. If the final salary is ₹54,450, what was the original salary?
Practice 16hard
A merchant buys goods at ₹5,000. He marks up the price by 40% but gives a discount of 25% on the marked price. Later, he increases the discounted price by 20%. What is his overall profit or loss percentage?
Practice 17hard
A shopkeeper marks up goods by 60% above cost price. He then offers a discount of 25% on the marked price. Later, due to a seasonal sale, he reduces the selling price by another 20%. What is his overall profit or loss percentage?
Practice 18hard
A product's price was reduced by 15% to ₹2,550. Later, it was increased by 20% from this reduced price. Finally, it was reduced by 10% from the new price. What is the overall percentage change from the original price?
Practice 19hard
A shopkeeper increases the price of an item by 25% and then decreases it by 20%. If the final price is ₹1,200, what was the original price?
Practice 20hard
The price of a commodity increases by 25% in the first year. In the second year, it decreases by 20% of the new price. In the third year, it increases by 10% of the price at the end of year 2. If the original price was ₹800, what is the percentage change in price over the three years?