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PS: Integers

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PS: Integers

by nusa84 » Thu Jul 15, 2010 7:47 am
Hi,

I need some help understanding the logic of this problem, I more or less see it, but any explanations clearer than this would be helpful. Thanks!

The symbol <n> represents the product of all the positive even integers less than or equal n. For example, <8> = 8*6*4*2. What is the greatest prime factor between <20> + <22>?

A. 7
B. 11
C. 13
D. 19
E. 23

OA: E
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by kvcpk » Thu Jul 15, 2010 7:52 am
nusa84 wrote:Hi,

I need some help understanding the logic of this problem, I more or less see it, but any explanations clearer than this would be helpful. Thanks!

The symbol <n> represents the product of all the positive even integers less than or equal n. For example, <8> = 8*6*4*2. What is the greatest prime factor between <20> + <22>?

A. 7
B. 11
C. 13
D. 19
E. 23

OA: E
<20> = 20*18*... =k
<22> = 22*20*... = 22*k
sum = k+22k = 23k
So greatest prime is 23
pick E
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Posts: 8
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by nusa84 » Thu Jul 15, 2010 8:01 am
kvcpk wrote:
nusa84 wrote:Hi,

I need some help understanding the logic of this problem, I more or less see it, but any explanations clearer than this would be helpful. Thanks!

The symbol <n> represents the product of all the positive even integers less than or equal n. For example, <8> = 8*6*4*2. What is the greatest prime factor between <20> + <22>?

A. 7
B. 11
C. 13
D. 19
E. 23

OA: E
<20> = 20*18*... =k
<22> = 22*20*... = 22*k
sum = k+22k = 23k
So greatest prime is 23
pick E
OMG ... and I couldn't see it ... thanks!!!
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