What is LCM of x, 6, and 9

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Thonk02: Junior | Next Rank: 30 Posts; Posts: 18; Joined: Fri Jan 30, 2009 1:30 pm

by Thonk02 » Mon Jul 06, 2009 4:24 pm

What is LCM of X, 6, and 9

1. LCM of X and 6 is 30
2. LCM of X and 9 is 45

Answer is D. any help here appreciated.

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Source: Beat The GMAT — Data Sufficiency | Mon Jul 06, 2009 4:24 pm

tohellandback: Legendary Member; Posts: 752; Joined: Sun May 17, 2009 11:04 pm; Location: Tokyo; Thanked: 81 times; GMAT Score:680

by tohellandback » Mon Jul 06, 2009 5:42 pm

IMO D
1) X can be 5,15 or 30
in all cases LCM of x,6,and 9 is 90

2)X can be 5,15,45
in all cases LCM is 90

The powers of two are bloody impolite!!

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brick2009: Master | Next Rank: 500 Posts; Posts: 171; Joined: Mon Jun 01, 2009 8:59 pm; Thanked: 8 times

D

by brick2009 » Fri Jul 10, 2009 9:58 pm

1.) LCM of X,6 = 30 => x has to be 5 => so can find LCM of x,6,9 --> Suff

2.) Same logic, x = 5, hence can find the LCM of x,6,9--> Suff

Ans: D

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missrochelle: Master | Next Rank: 500 Posts; Posts: 117; Joined: Wed Jun 09, 2010 7:02 am

by missrochelle » Mon Aug 23, 2010 4:02 pm

Is the easiest way to do this problem create prime boxes for each? The MGMAT strategy guide uses a really complex system to figure out the possible overlap (a chart listing the prime factors and taking the highest power of each.)

If you use prime boxes, do you assume that the LCM holds ALL shared prime factors? Thus, any leftover (in this case, 5) are automatically attributed to X?

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