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Number Systems for CAT 2025: Concepts, Shortcuts, and Solved Examples

One of the most scoring topics in the CAT exam is the number system. The foremost requirement to solve questions from this topic is to have clear conceptual clarity and logical skills. 


 

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Number System for CAT 2025 is by far the most scoring and the easiest topic to cover from the quantitative aptitude section in the CAT exam. To solve questions correctly from this section, you must have a very clear conceptual understanding of mathematics and delve proper logical skills. Moreover, this is the only topic where the direct use of shortcut tricks are recommended by experts and previous year toppers. To begin with we recommend that you focus on understanding what are the different types of numbers, next what is divisibility, HCF and LCM etc. This will ultimately help you to have a clear glance of what is important in this chapter.

Also Read:CAT 2025 Safe Target Percentile for IIM Indore

Important Topics from Number System CAT

You can check the vital topics here.

  • HCF and LCM
  • Factorization
  • Numbers
  • Factors
  • Divisibility Rules
  • Last Two Digits
  • Base System
  • Unit Digits
  • Remainders
  • Cyclicity
  • Indices & Surds

Basic Concepts of Number System

You can go through the basics from the below table.

Basic Concepts

Explanation

Types of Numbers

  • Natural Numbers (N): 1, 2, 3
  • Whole Numbers (W): 0, 1, 2, 3
  • Integers (Z): … –3, –2, –1, 0, 1, 2
  • Rational Numbers (Q): Numbers of the form p/q (q ≠ 0), e.g. 2/3, –7/5.
  • Irrational Numbers: Cannot be expressed as p/q, e.g. √2, π, e.
  • Real Numbers (R): All rational + irrational numbers.
  • Prime Numbers: Divisible only by 1 and itself. (e.g. 2, 3, 5, 7, 11…)
  • Composite Numbers: Numbers with more than two factors.
  • Even & Odd Numbers: Even = divisible by 2, Odd = not divisible by 2.

Divisibility Rules

  • By 2: Last digit even.
  • By 3: Sum of digits divisible by 3.
  • By 4: Last two digits divisible by 4.
  • By 5: Last digit 0 or 5.
  • By 6: Divisible by 2 and 3.
  • By 8: Last three digits divisible by 8.
  • By 9: Sum of digits divisible by 9.
  • By 11: Difference between sum of alternate digits divisible by 11.

HCF and LCM

  • HCF: Product of common prime factors with the smallest power.
  • LCM: Product of all prime factors with the highest power.
  • Relation =

HCF X LCM = Product of Numbers

Remainders & Modular Arithmetic

  • If N divided by m leaves remainder

R —> N ≡ r | M |

  • (a + b) mod m = [(a mod m) + (b mod m)] mod m
  • (a × b) mod m = [(a mod m) × (b mod m)] mod m
  • Useful in cyclicity of digits, unit’s place, remainder questions.

Cyclicity & Unit’s Digit

  • Cyclicity of powers helps find last digit quickly.
  • For unit digit → check cycle length, use exponent mod cycle.

Also Read:Common Executive MBA Application Questions and How to Answer Them

Formula Sheet Number System

Check the important formulas from this sheet.

Number System Formula Sheet -PDF Download

Quick Check before CAT Exam

You can go through this check list before the exam.

Properties of Operations

Details

Particulars

Cumulative Property of Addition

A + B = B + A

Associative Property of Addition

(A + B) + C = A + (B + C)

Cumulative Property of Multiplication

A x B = B x A

Associative Property of Multiplication

(A x B) X C = A X (B x C)

Distributive Property of Multiplication with respect to Addition

A x (B + C) = (A x B) + (A x C)

Law of Indices

Particulars

Details

anx an

am+n

am/ an

am-nif m > n

am/ an

1 / an-mif m < n

am/ an

a0= 1 if m = n

(am)n

amn= (an)m

Important Questions from Number System

Practice the following questions.

  1. If a 6-digit number is of the form 72A68B, and it is divisible by 88, find the value of A + B.

Ans = 12

  1. How many factors of 26 × 34 × 52are perfect squares?

Ans = 24

  1. Find the remainder when 798 is divided by 100

Ans = 49

  1. The product of two numbers is 10080, and their HCF is 48. Find the number of possible pairs of such numbers.

Ans = 0 pairs possible

  1. How many 3-digit numbers are divisible by 7 and have all digits distinct?

Ans = 100

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FAQs

Do last digit and unit digit questions appear often?

Yes, especially with exponents and cyclicity patterns are often asked in the exam.

What shortcuts are useful for Number System?

The shortcuts useful for CAT number system are Cyclicity of digits, Fermat&rsquo;s Little Theorem, Euler&rsquo;s Theorem, and factor-count formulas. &nbsp;

What is the best way to prepare for Number System in CAT?

The best way to prepare for number system in CAT follow- Master basics and properties (HCF, LCM, divisibility, remainders). Practice past year CAT questions (they often test conceptual depth). Use shortcuts like cyclicity, modular arithmetic, and factorization tricks. Avoid memorizing; instead, practice applying rules in different scenarios

How many questions on Number System usually appear in CAT?

Typically, 2&ndash;3 questions appear in CAT QA section, but the difficulty is moderate to high. Sometimes, questions are framed in disguised ways (remainders, factors, or base conversions). &nbsp;

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