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GMAT Prep - PS Number Properties

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by Sunny22uk » Wed Jul 02, 2008 9:17 pm
Is the answer p-1?

Lets take 5 as an example(5 is a prime number).The positive integers less than 5 are 1,2,3,4. Each of these numbers is not a factor of 5. so f(p) in this case is 4. i.e.e p-1.
Let me know if this is correct.
thanks
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by ksh » Wed Jul 02, 2008 10:34 pm
Let us analyze it by plugging nos.

From Ques stem f(n)<1 and has no positive factor common other than1

Choice 1. p-1
if p is a prime no. f(p)=1 when p=2,
f(p)=2, when p=3
f(p)=4, when p=5

it seems to satisfy the above two conditions. Correct

choice 2. p-2
f(p)=0, when p=2
f(p)=1, when p=3
f(p)=3, when p=5

from the above we see that it doesnot satisfy the necessary condition stated. incorrect

Similarly we can plugin values and see that only choice A satisfies the necessary condition
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by albertrahul » Sat Jul 05, 2008 7:12 am
Answer is P-1 (A)
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