CAT Practice : Number System - HCF, LCM

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Product of 2 numbers = LCM * HCF.

HCF LCM basics

    Q.8: There are 2 numbers such that a > b, HCF (a, b) = h and LCM (a, b) = l. What is the LCM of a – b and b?
    1. l
    2. (a - b) b
    3. (a - b) b / h
    4. h (a - b)


  • Correct Answer
    Choice C. (a - b) b / h

Detailed Solution

Given a > b, HCF = h, LCM = l
From the above we can say, HCF of (a – b, b) = h

LCM x HCF = Product of 2 numbers
(a – b)b = h x LCM
LCM = (a - b) b / h

Correct Answer: (a - b) b / h

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Number Theory is one of the most heavily tested topics. Within this, one should get the basics on factors, multiples, HCF, LCM very clear before moving on to the tougher sets.