The HCF and LCM of 12, 15 and 21 by applying the prime factorisation method is:

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3, 420

4,330

5,230

3,500

answer is A.

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Detailed Solution

Given three numbers are 12, 15 and 21.
Firstly, we have to find H.C.F, writing prime factors of all given numbers.

12 = 2 × 2 × 3 15 = 3 × 5 21 = 3 × 7

Since, only 3 is common factor of all number,
H.C.F = 3.
The formula for finding L.C.M is:
= Highest common factor × Product of remaining prime factors

= 3 × (2 × 2) × 5 × 7 = 420

L.C.M = 420
Hence, option 1 is correct.

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