Percentage — IBPS PO Prelims Study Notes

Overview

Percentage is the foundation of almost every arithmetic topic in IBPS PO Quantitative Aptitude. Questions on profit-loss, simple/compound interest, data interpretation, and even partnership are fundamentally percentage calculations in disguise. Mastering this topic means faster solving across 60–70% of the Quant section.

In IBPS PO Prelims, percentage appears directly in simplification, approximation, and DI sets. You'll rarely see a standalone "calculate 25% of 840" question—instead, percentages are embedded in word problems involving increase/decrease, successive changes, or ratio conversions. The key is to build mental math reflexes for common percentage-fraction equivalents and understand the logic of percentage change rather than memorising formulas mechanically.

Expect 3–5 questions per exam where percentage concepts are the core skill being tested, plus another 8–12 questions where percentage is a supporting calculation.

Key Concepts

• **Percentage means "per hundred"**: x% = x/100. This simple conversion is the basis of every calculation.

• **Percentage-to-fraction shortcuts save time**: Knowing that 25% = 1/4, 12.5% = 1/8, 33.33% = 1/3 lets you calculate mentally instead of on paper.

• **Percentage change has a direction**: Increase means adding to the base; decrease means subtracting. The formula always uses the *original* value as the base, not the new value.

• **Successive percentage changes don't simply add**: A 10% increase followed by a 10% decrease does NOT return you to the original—it results in a 1% net decrease.

• **"Of" means multiplication**: "What is 20% of 450?" translates to (20/100) × 450.

• **Percentage points vs. percentage change**: Going from 40% to 50% is a 10 percentage-point increase but a 25% relative increase.

• **Reverse percentage (finding the original)**: If a value after x% increase is A, then original = A × 100/(100 + x).

Formulas / Key Facts

**Basic Percentage Calculation** x% of N = (x × N) / 100

**Percentage Change** Percentage Change = [(New Value − Original Value) / Original Value] × 100

• Positive result = increase; Negative result = decrease

**Finding Original Value** If final value after x% increase = A, then Original = A × (100 / (100 + x)) If final value after x% decrease = A, then Original = A × (100 / (100 − x))

**Successive Percentage Change** Net effect of a% and b% successive changes = a + b + (ab/100)