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Quantitative AptitudeBeginner4 min study

How to Calculate Percentage Increase and Decrease in Exam Questions

प्रतिशत वृद्धि और कमी कैसे निकालें: आसान फॉर्मूला और ट्रिक्स

Percentage change measures the relative change between an initial (original) value and a new value expressed as a percentage. It is one of the most fundamental concepts tested across arithmetic, profit and loss, data interpretation, and population growth questions.

Key Rules & Core Formulas

Understand these foundational properties before solving questions

1Percentage Change Formula

Percentage Change = (|New Value - Original Value| / Original Value) × 100%

Always divide by the ORIGINAL (starting) value, never by the new value.

If New Value > Original Value, it is an Increase. If New Value < Original Value, it is a Decrease.
Standard Method

Step-by-Step Method to Solve

Follow these universal steps in order to solve any Quantitative Aptitude question accurately:

  1. 1

    Step 1: Identify Original Value and New Value

    Carefully identify which number represents the starting baseline (Original Value) and which is the final amount (New Value).

    Pro-Tip: Look for words like 'from ₹X to ₹Y' — the value after 'from' is always the original value.
  2. 2

    Step 2: Calculate the absolute difference

    Subtract the smaller value from the larger value to find the total change amount (Change = New - Original).

    Pro-Tip: Difference = |New Value - Original Value|.
  3. 3

    Step 3: Divide difference by Original Value

    Form the fraction: Difference / Original Value.

    Pro-Tip: The most common error is dividing by the new value instead of the original value.
  4. 4

    Step 4: Multiply by 100 to convert to percentage

    Multiply the fraction by 100% and simplify to find the final percentage change.

    Pro-Tip: Convert fractions to familiar percentages (e.g., 1/4 = 25%, 1/5 = 20%, 1/8 = 12.5%).

Worked Examples & Walkthroughs

Real questions solved step-by-step showing every calculation

1Example 1Method: Standard Formula Method

Question

The price of petrol increased from ₹80 per litre to ₹100 per litre. Find the percentage increase.

Step-by-Step Solution:

Step 1: Identify values:Original Value = ₹80, New Value = ₹100.
Step 2: Find difference:Increase = 100 - 80 = ₹20.
Step 3: Divide by original:Fraction = 20 / 80 = 1 / 4.
Step 4: Multiply by 100:Percentage Increase = (1 / 4) × 100% = 25%.
Final Result:
25% Increase
Exam Shortcut / Verification: Fraction shortcut: 20 is one-fourth (1/4) of 80, and 1/4 is always 25%.

Common Mistakes to Avoid

Avoid these frequent traps to protect yourself from negative marking

1

Dividing by the new value instead of the original value

Why it happens: Dividing by 100 instead of 80 gives 20%, which is wrong!
Correct approach: Always remember: the original value is the anchor of comparison.
Self-Assessment

Try It Yourself (Practice Questions)

Test your understanding on your own first, then reveal the step-by-step solution to check your work:

Practice #1

A student's score in mock tests improved from 60 marks to 75 marks. What is the percentage increase in score?

Quick Revision Summary

  • Percentage Change = (Difference / Original Value) × 100%.
  • Always divide by the starting/original value.
  • Use fraction-to-percentage shortcuts (1/2=50%, 1/3=33.3%, 1/4=25%, 1/5=20%).
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