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Gmatprep DS - LCM and GCF

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jayhawk2001: Community Manager; Posts: 789; Joined: Sun Jan 28, 2007 3:51 pmFollowed by: 1 member; Location: Silicon valley, California; Thanked: 30 times

by jayhawk2001 » Sat Jun 09, 2007 3:50 pm

OA after a few reply.

If n and t are positive integers, which is the greatest prime factor of product nt?

(1) The greatest common factor of n and t is 5
(2) The least common denominator of n and t is 105

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Source: Beat The GMAT — Data Sufficiency | Sat Jun 09, 2007 3:50 pm

f2001290: Master | Next Rank: 500 Posts; Posts: 400; Joined: Sat Mar 10, 2007 4:04 amFollowed by: 1 member; Thanked: 1 times

by f2001290 » Sun Jun 10, 2007 10:24 pm

Jay - Is it B?

The greatest prime factor can be 7. Though not sure.

Jay - Is Least Common Denominator same as Least Common Multiple?
I have never heard of LCD before.

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simplythebest: Junior | Next Rank: 30 Posts; Posts: 22; Joined: Mon Sep 18, 2006 10:17 am

by simplythebest » Mon Jun 11, 2007 10:33 pm

Its Just my call..not sure

In My Opinion(IMO) B

1. The greatest common factor is 5

so there can be n and t written as follows 5 * 19 and 5 * 23. So in this case the greatest Prime factor would be 23 as it can divide NT.

2. The LCM(I presume it as LCM) is 105 which is 5*3*7 and NT can be written as 105 * x and x cannot be PRIME because if X is prime the LCM will change...For example

21*5 = 105 assume that N=21 and T=55 (11 times 5) the LCM for N or T cannot be 105 and hence 7 is the largest prime divisor for NT.

Not sure about the logic..Maths gurus can correct me where i am wrong..

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simplythebest: Junior | Next Rank: 30 Posts; Posts: 22; Joined: Mon Sep 18, 2006 10:17 am

by simplythebest » Wed Jun 13, 2007 11:59 pm

Jay..any chance that my answer matches OA

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jayhawk2001: Community Manager; Posts: 789; Joined: Sun Jan 28, 2007 3:51 pmFollowed by: 1 member; Location: Silicon valley, California; Thanked: 30 times

by jayhawk2001 » Thu Jun 14, 2007 6:07 am

simplythebest wrote:Jay..any chance that my answer matches OA

Yup, the OA is B

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drhomler: Master | Next Rank: 500 Posts; Posts: 141; Joined: Thu May 03, 2007 1:15 pm

by drhomler » Thu Jun 14, 2007 6:18 am

I would go with B too(although with the OA posted I know Im not adding any new value there)

1)Highest common factor is five- as was said up above n could be five and t could be 5*19 so highest prime would be 19

2)if L common Denominator were 105 prime factors are 3, 5, 7 so n or t has to have 7 as a root and therefore 7 is the highest prime factor of nt

Answer B-anyone have a guess as tto the difficulty level of this problem?

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