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Senior Manager
Joined: 05 Mar 2006
Posts: 348

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10 Aug 2006, 17:44
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

Really stupid question:

Can somebody please explain the difference between LCM and GCD? Is there a formula?

Lets say A = 24 and B = 36

GCD = 12?

LCM = 12*3*2 = 72?

This was a simple one, but when it comes to fractions I get all messed up.

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Senior Manager
Joined: 05 Mar 2006
Posts: 348

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10 Aug 2006, 18:28
I found something pretty cool about GCD:

gcd(84,18) = 6

A much more efficient method is the Euclidean algorithm: divide 84 by 18 to get a quotient of 4 and a remainder of 12. Then divide 18 by 12 to get a quotient of 1 and a remainder of 6. Then divide 12 by 6 to get a remainder of 0, which means that 6 is the gcd.

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SVP
Joined: 30 Mar 2006
Posts: 1728

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11 Aug 2006, 00:27
To find LCM of fraction .......

Find LCM(x/y, m/n) = LCm (x,m)/HCF(y,n)

HFC (x/y, m/n) = HCF(x,m)/LCM(y,n)

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GMAT Club Legend
Joined: 07 Jul 2004
Posts: 5032

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Location: Singapore

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11 Aug 2006, 01:02
To find the HCF of 24 of 36, express both using prime factorization:

24 --> 2 * 2 * 2 * 3
36 --> 2 * 2 * 3 * 3

The HCF is thus 2 * 2* 3 = 12 (pick out the common terms)

To find the LCM, again express both using prime factorization:

The LCM is 2 * 2 * 2 * 3 * 3 = 72(pick out the common terms, then multiply in the remaining terms)

Kudos [?]: 456 [0], given: 0

11 Aug 2006, 01:02
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