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Number System (RRB)

Naturals, integers, rationals, divisibility rules, LCM/HCF, factorials, unit digits.

Practice — 9 questionsAsk AI

Number System (RRB) — Core

Naturals, integers, rationals, divisibility rules, LCM/HCF, factorials, unit digits.

Number system — quick reference for RRB
Notes

RRB-style number system topics:

  • Natural / Whole / Integers / Rationals / Reals — classification.
  • Divisibility rules (2, 3, 4, 5, 6, 7, 8, 9, 10, 11) — covered in Pack 16.
  • LCM × HCF = product of two numbers.
  • Co-prime: HCF = 1.
  • Unit digit cycles — 2:4 cycle (2,4,8,6); 3:4 cycle; 7:4; 9:2; 0/1/5/6 stay same.
  • Factorial trailing zeros: count factors of 5 in n!.

RRB-style frequent questions:

  1. Find LCM/HCF of two numbers.
  2. Smallest number to ADD to make divisible by X.
  3. Largest n-digit number divisible by Y.
  4. Unit digit of large powers.
  5. Find prime / composite property.

Practice approach: memorize first 20 primes. Master divisibility quickly.