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by unknown13 » Sun Nov 18, 2012 1:27 am
IMO Ans. Is 19
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by pritish2301 » Sun Nov 18, 2012 2:28 am
rupamroy wrote:What is the greatest prime factor of 12!11! + 11!10!?

(A) 7
(B) 11
(C) 13
(D) 17
(E) 19
solution:
12!11! + 11!10!
= 12 x 11 x 10! x 11! + 11!10!
= 11!10! (12 x 11 + 1)
= 11!10! (133)
check the options = 19 x 7 is 133
Hence greatest is 19.

Answer E
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by rupamroy » Tue Nov 20, 2012 6:53 am
Yes, Answer is E) 19
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by Bill@VeritasPrep » Tue Nov 20, 2012 10:31 am
pritish2301 wrote:
rupamroy wrote:What is the greatest prime factor of 12!11! + 11!10!?

(A) 7
(B) 11
(C) 13
(D) 17
(E) 19
solution:
12!11! + 11!10!
= 12 x 11 x 10! x 11! + 11!10!
= 11!10! (12 x 11 + 1)
= 11!10! (133)
check the options = 19 x 7 is 133
Hence greatest is 19.

Answer E
Exactly. Really, this is a fairly straightforward factoring question, but it's made pretty difficult by giving you factorials instead of terms that you're used to factoring, like variables.
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by rupamroy » Tue Nov 20, 2012 5:22 pm
V True bill.. and I have also noticed a definite shift in the characteristic of PS questions in GMAT. It was not so long ago, that PS used to test more of mathematical ability than logic intertwined with maths ability. But after going through the GMAT Prep 1, I feel there is now more stress on reasoning and on cognitive abilities. I should admit, I have myself made mistakes on a couple of those. Would post them separately.
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by Bill@VeritasPrep » Tue Nov 20, 2012 6:19 pm
True. I think the shift is a good thing; you are rewarded more for actually leaning than for simply memorizing.
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