Quantitative Aptitude
Percentage
Percentage
Percentage means 'per hundred'. Any percentage is a fraction with denominator 100. The ability to convert fluently between %, fraction, and decimal is the foundation of all percentage problems.
Key Idea
Always divide by the ORIGINAL (base) value — never by the new value — when computing percentage change.
Core Formulas
Find X% of a number
(X / 100) × N
When asked to find what X% of a given number N is.
Percentage Change
Change% = (Change / Original) × 100
When a value increases or decreases and you need the % change.
Find Original from Changed Value
Original = Result × 100 / (100 ± Change%)
When you know the final value after a % change and need the original.
Successive Percentage Changes
Net% = a + b + (ab / 100)
When two percentage changes (a% then b%) are applied one after another.
Base Equivalence
X% of Y = Y% of X
When one of the two values is easier to work with as the base.
Relevant Exams
Percentage appears in 3–4 questions in every SSC CGL, IBPS PO, and SBI PO paper. It is also the foundation for Profit & Loss and SI/CI topics.