Number System — Revision Notes
XAT · Quantitative Ability & Data Interpretation
Free Number System revision notes for XAT Quantitative Ability & Data Interpretation 2026 — key concepts, formulas, and definitions for quick revision.
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Key concepts, formulas, and definitions from Number System for XAT Quantitative Ability & Data Interpretation preparation.
Key Topics to Revise
Types of Numbers and Basic Definitions
- Natural Numbers (N): 1, 2, 3, 4... - used for counting, smallest is 1
- Whole Numbers (W): 0, 1, 2, 3... - natural numbers plus zero
- Integers (Z): ...-3, -2, -1, 0, 1, 2, 3... - positive and negative whole numbers
Prime Number Properties and Testing
- Smallest prime: 2 (only even prime)
- Smallest odd prime: 3
- Prime checking: Test divisibility only by primes ≤ √n
GCD and LCM Concepts
- GCD (HCF): Largest number that divides all given numbers
- LCM: Smallest number that is divisible by all given numbers
- For two numbers: GCD × LCM = Product of numbers
Divisibility Rules and Tests
- Divisibility by 2: Last digit is even (0,2,4,6,8)
- Divisibility by 3: Sum of digits divisible by 3
- Divisibility by 4: Last two digits form number divisible by 4
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