Quantitative Aptitude — Fundamentals

Number System — the foundation everything else builds on

Before formulas, get genuinely fast at basic number properties: divisibility rules (a number's divisible by 3 if its digit sum is divisible by 3; by 4 if its last two digits form a number divisible by 4; by 9 if its digit sum is divisible by 9 — memorize these, don't re-derive them under time pressure), HCF/LCM via prime factorization, and recognizing perfect squares/cubes on sight. This sounds basic, but slow number-sense is what actually causes slow performance on "harder" topics later — the bottleneck usually isn't the advanced formula, it's slow arithmetic underneath it.

Simplification & Approximation — BODMAS under time pressure

The rule (Brackets, Orders/exponents, Division, Multiplication, Addition, Subtraction) is simple; applying it fast on a multi-step expression under a 20-second budget is the actual skill. Practice specifically on expressions combining fractions, percentages, and brackets together — that combination is what actually appears in exam questions, not clean single-operation problems.

Percentages — the most reused concept across every other topic

Percentage isn't an isolated topic — it's the language Profit & Loss, Simple/Compound Interest, and Data Interpretation are all expressed in. Getting genuinely fast at percentage-to-fraction conversion (25% = 1/4, 33.33% = 1/3, 12.5% = 1/8, and so on) pays off across every one of those topics, not just percentage questions themselves — this is why Overview's speed-techniques section calls this out specifically as high-leverage.

Profit & Loss — the core formulas, precisely

•Profit % = (Profit / Cost Price) × 100

•Loss % = (Loss / Cost Price) × 100

•Selling Price = Cost Price × (1 + Profit%/100), or × (1 − Loss%/100)

The common trap: profit/loss percentage is always calculated on Cost Price, not Selling Price — a genuinely frequent source of wrong answers is applying the percentage to the wrong base value under time pressure.

Simple Interest vs. Compound Interest — the actual formula difference

•Simple Interest: SI = (P × R × T) / 100 — interest is calculated only on the original principal, every period.

•Compound Interest: A = P × (1 + R/100)^T — interest is calculated on the accumulated amount (principal + previously earned interest), which is why it grows faster over time.

For a 2-year period specifically, there's a useful shortcut: CI − SI = P × (R/100)² — worth memorizing directly rather than computing both full formulas separately when a question specifically involves a 2-year CI/SI difference.

Ratio, Proportion & Averages

Ratios are comparative, not absolute — A:B = 2:3 means A is 2 parts and B is 3 parts of some common unit, not that A = 2 and B = 3 literally. The most common exam application is combining two ratios sharing a common term (see Overview's A:B, B:C → A:C example) — the technique is making the shared term's value equal across both ratios before combining, not adding or multiplying the ratios directly.

Time, Speed & Distance — the relative speed concept

Speed = Distance / Time is the base formula; the exam-relevant complexity is relative speed: when two objects move toward each other, relative speed = sum of their speeds; when moving in the same direction, relative speed = difference of their speeds. Train-crossing-a-pole/platform/another-train questions (like Overview's PYQ-pattern example) are almost entirely applications of this one relative-speed concept, not a separate topic requiring separate formulas.