Prime Factors!!!

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kath_the_great4: Junior | Next Rank: 30 Posts; Posts: 24; Joined: Mon May 19, 2008 3:48 pm

by kath_the_great4 » Sat Sep 27, 2008 7:20 am

What is the greatest Prime Factor of 4^17-4^28?

I guessed and got this one right, but I can't keep rellying on the low odds of guessing so can someone please explain how to handle questions of this nature?

Thanks in advance!

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Source: Beat The GMAT — Problem Solving | Sat Sep 27, 2008 7:20 am

sudhir3127: Legendary Member; Posts: 829; Joined: Mon Jul 07, 2008 10:09 pmFollowed by: 3 members; Location: INDIA; Thanked: 84 times

Re: Prime Factors!!!

by sudhir3127 » Sat Sep 27, 2008 8:48 am

kath_the_great4 wrote:What is the greatest Prime Factor of 4^17-4^28?

I guessed and got this one right, but I can't keep rellying on the low odds of guessing so can someone please explain how to handle questions of this nature?

Thanks in advance!

Please use the search option before starting a new thread. amd please post the Question correctly..
AFAI remember the Question shud be

4^17- 2^28

4^17 is 2^34

2^34-2^28

2^28( 2^6-1)

2^28 * 63

highest prime factor of 63 is 7

hence its 7.

Please let me know if u have any doubts.......

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kath_the_great4: Junior | Next Rank: 30 Posts; Posts: 24; Joined: Mon May 19, 2008 3:48 pm

by kath_the_great4 » Sat Sep 27, 2008 9:38 am

Thanks for that!

Exponents are my weak point so there is one thing I wanted to clarify---
why are we ignoring 2^28 when picking the greatest prime factor of this product?

Does anyone have any links to intermediate/advanced rules of exponents? Would be greatly appreciated.

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stop@800: Legendary Member; Posts: 871; Joined: Wed Aug 13, 2008 7:48 am; Thanked: 48 times

by stop@800 » Sat Sep 27, 2008 10:30 am

2^28 has only one prime factor which is 2.

www.interrogationpoint.com

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mberkowitz: Senior | Next Rank: 100 Posts; Posts: 76; Joined: Sun Jul 20, 2008 10:47 am; Location: new york city; Thanked: 1 times

by mberkowitz » Mon Sep 29, 2008 8:58 am

kath check out directory of gmat resources under resources tab, if you look under the math area I believe they have a compilation of rules on exponents...

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stop@800: Legendary Member; Posts: 871; Joined: Wed Aug 13, 2008 7:48 am; Thanked: 48 times

by stop@800 » Mon Sep 29, 2008 11:16 am

mberkowitz wrote:kath check out directory of gmat resources under resources tab, if you look under the math area I believe they have a compilation of rules on exponents...

Thanks a lot mberkowitz.
I was also not aware of this excellent material.

www.interrogationpoint.com

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mberkowitz: Senior | Next Rank: 100 Posts; Posts: 76; Joined: Sun Jul 20, 2008 10:47 am; Location: new york city; Thanked: 1 times

by mberkowitz » Mon Sep 29, 2008 11:19 am

stop are u being facitious?

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