GMAT Prep Question

[bjahn]

The function f is defined for all positive integers 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

I dont get why the answer is a, i thought it would be b

[cris]

It has to be p-1 because you count 1. With p-2 you will not be counting 1.

Correct me if I am wrong

[bjahn]

But doesn't the question say "other than 1" ?? Doesn't this mean 1 should not be counted?

[Stuart@KaplanGMAT]

But doesn't the question say "other than 1" ?? Doesn't this mean 1 should not be counted?

1 is a positive integer that has no factors in common with n other than 1 (the "other than 1" refers to the factors, not to the integer itself). Therefore, count 1.