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dunkin77
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 Posted: Mon Jun 18, 2007 3:22 pm Post subject: PREP |
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What is the greatest prime factor of 2^100 - 2^96?
A. 2
B. 3
C. 5
D. 7
E. 11
CAN ANYONE HELP?
Last edited by dunkin77 on Tue Jun 19, 2007 3:18 am; edited 2 times in total |
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jayhawk2001
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| Posted: Mon Jun 18, 2007 4:19 pm Post subject: Re: PREP |
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| dunkin77 wrote: | What is the greatest prime factor of 2100 - 296?
A. 2
B. 3
C. 5
D. 7
E. 11
CAN ANYONE HELP? |
Hmm, 2100-296 = 1804 = 4 * 451 = 4 * 11 * 41
I'm getting 41 as the greatest prime factor... |
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moneyman
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| Posted: Tue Jun 19, 2007 1:06 am Post subject: |
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Here is my approach..
2100-296 is 1804
1804 is 11*164 and since the greatest prime from the given options is asked..I think the answer would be E..Am I right??
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dunkin77
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| Posted: Tue Jun 19, 2007 3:19 am Post subject: |
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Sorry, I think I wrote it wrong. 
It's 2^100 - 2^96 . |
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gabriel
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| Posted: Tue Jun 19, 2007 5:17 am Post subject: |
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| dunkin77 wrote: | Sorry, I think I wrote it wrong.
It's 2^100 - 2^96 . |
.. so that wuld be 2^96(2^4-1) = 2^96*15 .. so the prime factors fro this number are 2,3,5 ... and the highest is 5 .. |
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dunkin77
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| Posted: Tue Jun 19, 2007 5:58 am Post subject: |
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| you're right - thank you:) |
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pgarg00
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| Posted: Wed Jul 04, 2007 6:07 pm Post subject: ans |
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2^96(2^4 -1)
2^96(16-1)
2^96(3*5)
greates prime factor is 5 |
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