33 days
Start free

Inequalities & Modulus for CAT: Formulas, Weightage & Question Types

Modulus equations, maxima and minima, and counting integer solutions.

Inequalities & Modulus formula sheet

Everything CAT needs from Inequalities & Modulus, in one place. Bookmark it for revision; the lesson in the app explains where each line comes from and when to reach for it.

Everything for this chapter, in one place. xx is real throughout.

Modulus — the basics

Definition∣x∣=x\lvert x \rvert = x if x≥0x \ge 0, and −x-x if x<0x < 0
Always∣x∣≥0\lvert x \rvert \ge 0 and ∣x∣2=x2\lvert x \rvert^2 = x^2
Products∣ab∣=∣a∣∣b∣\lvert ab \rvert = \lvert a \rvert \lvert b \rvert
What it means∣x−c∣\lvert x - c \rvert is the distance from xx to cc

Solving with a modulus

∣x∣=a\lvert x \rvert = a, a>0a > 0x=ax = a or x=−ax = -a
∣x∣<a\lvert x \rvert < a, a>0a>0−a<x<a-a < x < a
∣x∣>a\lvert x \rvert > a, a>0a>0x<−ax < -a or x>ax > a
∣x∣=a\lvert x \rvert = a, a<0a < 0no solution
∣f(x)∣=g(x)\lvert f(x) \rvert = g(x)needs g(x)≥0g(x) \ge 0 — check every root against this

Two moduli

Triangle inequality∣a+b∣≤∣a∣+∣b∣\lvert a+b \rvert \le \lvert a \rvert + \lvert b \rvert, equal exactly when aa and bb have the same sign
Reverse form∣∣a∣−∣b∣∣≤∣a−b∣\bigl\lvert \lvert a \rvert - \lvert b \rvert \bigr\rvert \le \lvert a - b \rvert
Sum of two distances∣x−p∣+∣x−q∣≥∣p−q∣\lvert x-p \rvert + \lvert x-q \rvert \ge \lvert p-q \rvert, equal exactly when xx lies between pp and qq
Worth memorising∣x+y∣+∣x−y∣=2max⁡(∣x∣,∣y∣)\lvert x+y \rvert + \lvert x-y \rvert = 2\max(\lvert x \rvert, \lvert y \rvert)

Sign charts — how every rational inequality is solved

Methodfactor into linear pieces, mark every root and every break, test one point, alternate
Odd power of a factorthe sign flips across that root
Even power of a factorthe sign does not flip
Denominator rootsalways excluded, drawn hollow, even when the inequality is ≤\le or ≥\ge
Never do thiscross-multiply by a quantity whose sign you do not know

AM–GM and friends — for positives

Two termsa+b2≥ab\dfrac{a+b}{2} \ge \sqrt{ab}, equal only when a=ba=b
The workhorset+1t≥2t + \dfrac{1}{t} \ge 2 for t>0t>0, and ≤−2\le -2 for t<0t<0
General two-termkt+mt≥2kmkt + \dfrac{m}{t} \ge 2\sqrt{km} for t>0t>0
Squaresx2+y2≥2∣xy∣x^2 + y^2 \ge 2\lvert xy \rvert
Fixed sumthe product is largest when the numbers are equal
Fixed productthe sum is smallest when the numbers are equal
Cauchy–Schwarz(ax+by)2≤(a2+b2)(x2+y2)(ax+by)^2 \le (a^2+b^2)(x^2+y^2), equal exactly when ay=bxay = bx

Quadratic maxima and minima — see the Quadratic chapter

Extreme value of ax2+bx+cax^2+bx+c−D4a-\dfrac{D}{4a}, reached at x=−b2ax = -\dfrac{b}{2a}

The 5 Inequalities & Modulus question types CAT repeats

Past CAT papers return to the same few shapes. Learn to recognise them and most questions become a known routine. Beyond these, CAT has asked 3 rarer one-off shapes here.

  1. 01

    A modulus equation — split at the critical points

  2. 02

    Two moduli added — read it as distance

  3. 03

    Find a maximum or a minimum

  4. 04

    A rational or quadratic inequality — chart the signs

  5. 05

    Count the integer solutions

Is Inequalities & Modulus costing you marks?

Take the free diagnostic to see where you stand in Inequalities & Modulus and every other high-weight chapter, then learn, practise and prove it on fresh questions.

Take the free diagnostic

No sign-up needed. Your first chapter is free end to end.

Inequalities & Modulus in CAT: quick answers

How many Inequalities & Modulus questions come in CAT Quant?
About 1.3 questions in a 22-question Quant section, worth roughly 4 marks. Inequalities & Modulus appeared in 21 of the 24 CAT papers from 2017 to 2025, 34 questions in all, which ranks it 4 of 25 Quant chapters.
Are Inequalities & Modulus questions in CAT MCQ or TITA?
38% of the Inequalities & Modulus questions asked since 2017 were TITA (type in the answer, no negative marking). The rest were multiple choice.
What types of Inequalities & Modulus questions does CAT ask?
CAT keeps returning to 5 question shapes in Inequalities & Modulus: A modulus equation — split at the critical points; Two moduli added — read it as distance; Find a maximum or a minimum; A rational or quadratic inequality — chart the signs; Count the integer solutions.

More Algebra for CAT