GMATPrep 2 question

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GMATPrep 2 question

by bkobilov » Tue Sep 28, 2010 7:57 am
Hi guys, pls help with this question.

The function f is defined for all positive integers n by the following rule: f(n) is the number of positive integers each of which is less than n and has no positive factor in common with n other than 1. If p is any prime number then f(p)=

a. p-1
b. p-2
c. (p+1)/2
d. (p-1)/2
e. 2

Have no idea how to approach this question.
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by shovan85 » Tue Sep 28, 2010 8:26 am
A

f(n) is number of integers < n and no common factor except 1

if p is a prime number then all the integers less than p will be in the list as they will not have any common factor with p except1

as the list will be always < p we can minus 1 from the list so p-1

can verify by taking any prime number