Three ways to calculate a percentage
X% of Y — find a portion of a number (e.g. 18% of ₹2,400 for a restaurant tip). X is what % of Y — find what share one number is of another (e.g. marks scored out of total marks). % change — find the percentage increase or decrease between two numbers (e.g. price before and after a discount, or salary before and after a hike).
Common uses
Exam marks and percentages, discounts and sale prices, tax and tip calculations, salary hikes, profit/loss margins, and interest calculations all reduce to one of these three questions.