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Factorial and primes

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by winniethepooh » Wed Jul 13, 2011 11:46 am
What is the greatest prime factor of 12!11! + 11!10!?

(A) 7
(B) 11
(C) 13
(D) 17
(E) 19
Last edited by winniethepooh on Wed Jul 13, 2011 12:31 pm, edited 1 time in total.
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Source: — Problem Solving |

by Frankenstein » Wed Jul 13, 2011 11:55 am
Hi,
12!11! + 11!10! = 11!10!(11*12 + 1) = 11!10!*133 = 11!10!*7*19

Hence, E
Btw, where is probability in this?
Cheers!

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by winniethepooh » Wed Jul 13, 2011 12:25 pm
Oops, drop that!
:oops:
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by amit2k9 » Wed Jul 13, 2011 9:59 pm
(10!)^2*11[12*11+1] = (10!)^2*11 * 133

133= 7*19.
hence 19.
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