smallest prime

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cmr209: Senior | Next Rank: 100 Posts; Posts: 42; Joined: Thu Sep 11, 2008 11:07 pm; Location: California; Thanked: 3 times

by cmr209 » Mon Aug 17, 2009 10:25 pm

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Source: Beat The GMAT — Problem Solving | Mon Aug 17, 2009 10:25 pm

prindaroy: Master | Next Rank: 500 Posts; Posts: 113; Joined: Thu Jul 16, 2009 11:23 am; Thanked: 15 times; GMAT Score:730

by prindaroy » Tue Aug 18, 2009 12:03 pm

The answer E. this question has been asked before but I don't where the thread is but anyways;

h(100) = 2*4*6*................*100

= 2(1*2*3*4................*50)

so for a divisor of h(100) + 1, to happen, it would have to be greater than 50 or in this case 40.

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winnerhere: Master | Next Rank: 500 Posts; Posts: 231; Joined: Thu Apr 12, 2007 2:45 amFollowed by: 1 member; Thanked: 5 times

by winnerhere » Tue Aug 18, 2009 11:47 pm

prindaroy wrote:The answer E. this question has been asked before but I don't where the thread is but anyways;

h(100) = 2*4*6*................*100

= 2(1*2*3*4................*50)

so for a divisor of h(100) + 1, to happen, it would have to be greater than 50 or in this case 40.

could u please explain the last line please.

and in the previous step its 2^50...u cant take just 2 out as its not summation but multiplication inside the bracket.

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prindaroy: Master | Next Rank: 500 Posts; Posts: 113; Joined: Thu Jul 16, 2009 11:23 am; Thanked: 15 times; GMAT Score:730

by prindaroy » Tue Aug 18, 2009 11:51 pm

Okay,

so ever number from 1 to 50 will divide h(100) right? But not one of those numbers will divide h(100)+1, because they already divide h(100). So the smallest number that will do so, has to be greater than 50. In the choices given, greater than 40 is the only choice that reflects our solution. So E is the answer

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

by tohellandback » Wed Aug 19, 2009 12:00 am

this question has been discussed a zillion times..
Please go here

https://www.beatthegmat.com/gmat-prep-q-t14339.html

The powers of two are bloody impolite!!

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winnerhere: Master | Next Rank: 500 Posts; Posts: 231; Joined: Thu Apr 12, 2007 2:45 amFollowed by: 1 member; Thanked: 5 times

by winnerhere » Wed Aug 19, 2009 12:04 am

prindaroy wrote:Okay,

so ever number from 1 to 50 will divide h(100) right? But not one of those numbers will divide h(100)+1, because they already divide h(100). So the smallest number that will do so, has to be greater than 50. In the choices given, greater than 40 is the only choice that reflects our solution. So E is the answer

great understood

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