It is currently 20 Nov 2017, 23:38

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

The function f is define for all positive integers n by the

Author Message
Manager
Joined: 28 Dec 2005
Posts: 117

Kudos [?]: 3 [0], given: 0

The function f is define for all positive integers n by the [#permalink]

Show Tags

26 Feb 2006, 16:51
00:00

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions

HideShow timer Statistics

This topic is locked. If you want to discuss this question please re-post it in the respective forum.

The function f is define for all positive integers n by the folling 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 than f(p) =
A. p-1
B. P-2
C. (P+1)/2
D. (P-1)/2
E. 2

Kudos [?]: 3 [0], given: 0

GMAT Club Legend
Joined: 07 Jul 2004
Posts: 5032

Kudos [?]: 453 [0], given: 0

Location: Singapore

Show Tags

26 Feb 2006, 18:36
If p is 2, f(p) = 1
If p is 3, f(p) = 2
If p is 5, f(p) = 3
If p is 7, f(p) = 4

I think C should fit in.

Kudos [?]: 453 [0], given: 0

Manager
Joined: 14 Jun 2005
Posts: 99

Kudos [?]: 20 [0], given: 0

Show Tags

27 Feb 2006, 09:24
ywilfred wrote:
If p is 2, f(p) = 1
If p is 3, f(p) = 2
If p is 5, f(p) = 3
If p is 7, f(p) = 4

I think C should fit in.

isn't f(5)=4? 1, 2, 3, 4 all of which are less than 5 and has no positive factor in common with 5.

I think A

Kudos [?]: 20 [0], given: 0

SVP
Joined: 24 Sep 2005
Posts: 1883

Kudos [?]: 386 [0], given: 0

Re: PS - question from GMATprep [#permalink]

Show Tags

27 Feb 2006, 10:21
myc2004 wrote:
The function f is define for all positive integers n by the folling 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 than f(p) =
A. p-1
B. P-2
C. (P+1)/2
D. (P-1)/2
E. 2

it's clearly that for every prime number p, there're (p-1) numbers from 1 to p-1 which has no common positive factors other than 1 with p.
To make it clearly:
1 and p have only 1 common (+) factor
2 and p have only 1 common (+) factor
.......................................................
(p-1) and p have only 1 common (+) factor.

Look at those provided answer choices:
1)p-2 and (p-1)/2 both are smaller than p-1 ...that means they don't indicate the maximum number of cases which satisfy the problem. ---> eliminate!
2) taking p=2 --> (p+1) is odd ---> (p+1)/2 is not integer ---> unreasonable ---> eliminate this choice
3) also take p=2 ---> f(p) = 1 ----> E can't be the OA

Only A left unbreakable ---> A it is.

Kudos [?]: 386 [0], given: 0

Manager
Joined: 28 Dec 2005
Posts: 117

Kudos [?]: 3 [0], given: 0

Show Tags

27 Feb 2006, 14:48
OA is A thanks for explaining

Kudos [?]: 3 [0], given: 0

27 Feb 2006, 14:48
Display posts from previous: Sort by