CAT Number System - Comprehensive Study Notes

CAT Number System: Formula Book & Strategy Guide

1. Classification of Numbers & Basic Properties

[VIDEO: "CAT Remainder Theorem and Cyclicity shortcuts"]

When to Attempt: Divisibility, HCF/LCM, Remainder (using cyclicity), Trailing Zeroes, and basic factor problems are generally quick and high-probability. Attempt these first.
When to Skip/Be Cautious: Lengthy successive division/CRT problems, complex base conversion with operations, and questions involving heavy algebraic manipulation with unknowns. Skip if they seem time-consuming (>2.5 mins).
Time Allocation: Spend no more than 2-2.5 minutes per Number System question. Use shortcut rules and mental math for cyclicity and divisibility.
Common Trap Avoidance: Always check the domain (natural/integer) asked. Remember 1 is not prime. For "number of factors", ensure you use (power+1). In HCF*LCM, remember it's only for two numbers.
Practice Approach: Start with easy problems on factors/divisibility, move to moderate remainder/cyclicity, then tackle hard problems involving combinations of concepts (e.g., remainders + factorials).

Final Tip: Master the art of elimination using units digits and divisibility rules to solve questions without full calculation.