Percentage
Percentage
Percentage means \u2018per hundred\u2019 and underpins Profit & Loss, SI/CI, and Data Interpretation. SSC CGL, IBPS PO, and SBI PO each carry 3\u20134 percentage questions per paper. Exams test successive changes, reverse-percentage (find original from final), and fraction\u2013percent conversion speed. Always divide by the original value when computing percentage change \u2014 this is the most common trap.
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
Multiply the number by X/100 \u2014 convert X to a fraction (e.g. 12.5% = 1/8) for mental math speed.
Percentage Change
Change% = (Change / Original) × 100
Divide the absolute change by the original (base) value, not the new value \u2014 then multiply by 100 to get the percentage increase or decrease.
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.