Is there a shortcut to find HCF and LCM quickly for GMAT questions?

Question

T Mehta · Accepted Answer

There is ,  and it&rsquo;s more efficient than people expect, especially when the numbers don&rsquo;t share many obvious factors.
&bull; Use prime factorization for clean, small numbers like 12, 36, or 60 &mdash; it's quick once you're familiar. &bull; When the numbers are larger or awkward, this works better: &emsp;LCM = (a &times; b) / HCF &bull; For example, with 16 and 20: &emsp;HCF = 4 &rarr; LCM = (16 &times; 20) &divide; 4 = 80 &bull; This method saves time and avoids writing full factor trees, especially for pairs like 45 and 64. &bull; GMAT usually sticks to numbers below 100, so both approaches are manageable with a bit of practice.
Know both methods and choose based on how clean the numbers look in the question.
For more details you can read this blog on "Concepts of LCM HCF GMAT"

B.K Sharma · Answer

Yes, the fastest way to find both HCF and LCM on GMAT questions is using prime factorization &mdash; it&rsquo;s quick, consistent, and works well when the numbers are small or easy to break down.
Break each number into its prime factors. For HCF, take the lowest powers of common primes. For LCM, take the highest powers of all primes involved.
Example: 18 = 2 &times; 3&sup2; 24 = 2&sup3; &times; 3 HCF = 2 &times; 3 = 6 LCM = 2&sup3; &times; 3&sup2; = 72
This method is most useful when numbers are under 100. For larger or odd numbers, it can slow you down, so it&rsquo;s good to combine it with estimation or other strategies when needed. Practicing factor recognition (2, 3, 5, 7) helps build speed for test day.