Understanding Number System for Bank Exams
Number System Mastery (Professional Level)
Number System is the foundation of quantitative aptitude. Strong understanding helps solve multiple topics faster.
1. Types of Numbers
- Natural Numbers: 1, 2, 3...
- Whole Numbers: 0, 1, 2...
- Integers: -3, -2, -1, 0, 1...
- Rational Numbers: p/q
- Irrational Numbers: √2, π
2. Divisibility Rules (Important)
- 2 → Last digit even
- 3 → Sum of digits divisible by 3
- 4 → Last 2 digits divisible by 4
- 5 → Ends with 0 or 5
- 9 → Sum divisible by 9
3. Digital Root Trick
Add digits until single digit remains.
Example: 987 → 9+8+7 = 24 → 2+4 = 6
Used to check answers quickly in exams
4. LCM & HCF (Core Concept)
LCM × HCF = Product of numbers
Example: 12 × 18 = 216 LCM = 36, HCF = 6
Derivation: Numbers = HCF × Co-prime numbers
5. Remainder Concept
(a + b) mod n = (a mod n + b mod n)
Example: (23 + 45) mod 5 = 68 mod 5 = 3
6. Unit Digit Trick
Find last digit pattern.
Example: 2⁵ = 32 → Unit digit = 2 Pattern: 2,4,8,6 repeat
Speed Strategy
- Memorize divisibility rules
- Use digital root for checking
- Practice remainder logic
- Learn unit digit patterns
Practice Questions
1. Check 432 divisible by 3?
2. Find digital root of 999
3. Find remainder of 27 ÷ 4
4. Unit digit of 3⁴?
Strong Basics Build Strong Results
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