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 Your Progress

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

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

It appears that you are browsing the GMAT Club forum unregistered!

Signing up is free, quick, and confidential.
Join other 350,000 members and get the full benefits of GMAT Club

Registration gives you:

Tests

Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.

Applicant Stats

View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more

Books/Downloads

Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

If, for all positive integer values of n, P(n) is defined as [#permalink]
25 Apr 2013, 21:43

1

This post received KUDOS

4

This post was BOOKMARKED

00:00

A

B

C

D

E

Difficulty:

65% (hard)

Question Stats:

59% (02:42) correct
41% (01:27) wrong based on 96 sessions

If, for all positive integer values of n, P(n) is defined as the sum of the smallest n prime numbers, then which of the following quantities are odd integers?

I. P(10) II. P(P(10)) III. P(P(P(10)))

(A) I only (B) I and II only (C) I and III only (D) II and III only (E) I, II, and III

Re: If, for all positive integer values of n, P(n) is defined as [#permalink]
25 Apr 2013, 22:41

Expert's post

emmak wrote:

If, for all positive integer values of n, P(n) is defined as the sum of the smallest n prime numbers, then which of the following quantities are odd integers? I. P(10) II. P(P(10)) III. P(P(P(10)))

(A) I only (B) I and II only (C) I and III only (D) II and III only (E) I, II, and III

Express appreciation by pressing KUDOS button

2 is the only even prime number. Now, the sum of first 10 prime numbers = 9*odd + 2 = odd. Thus P(10) = odd.

Again, the sum of the first n -odd primes = (n-1)*odd+2 = even.Thus, p(P(10)) = even.

Similarly, the sum of the first m - even primes = (m-1)*odd+2 = odd.

Re: If, for all positive integer values of n, P(n) is defined as [#permalink]
25 Apr 2013, 23:03

3

This post received KUDOS

Expert's post

1

This post was BOOKMARKED

emmak wrote:

If, for all positive integer values of n, P(n) is defined as the sum of the smallest n prime numbers, then which of the following quantities are odd integers? I. P(10) II. P(P(10)) III. P(P(P(10)))

(A) I only (B) I and II only (C) I and III only (D) II and III only (E) I, II, and III

Express appreciation by pressing KUDOS button

This kind of question can give students fits. The key is to figure out what is being asked. The function P is summing up the first N prime numbers, so for example P(3) = 2 + 3 + 5. The total is 10. If I picked P(4), I'd get the same sum + 7, or 17.

Since the question hinges on whether the sum is even or odd, the only number that's unique in this circumstance is 2, as it is the only even prime number in an otherwise homogenous sea of odd numbers. Thus P(1) is even, P(2) is odd, P(3) is even again and P(4) is odd again. This is the pattern, so clearly P(10) will be 2 + nine odd numbers, so it will be odd. We can eliminate D.

P(P(10)) is where this starts getting interesting. You're doing the same test on a number we don't exactly know, but we know it must be odd. Since we know the pattern, the odd number will give us even. P(P(10)) will not be odd, eliminate B and E.

P(P(10))) will be the same function over a number we just calculated would be even. Hence it must be odd again. Eliminate A, the answer must be C.

Function questions are among the least understood questions on the GMAT, and this type of question can get people spending 3-4 minutes extrapolating numbers. If you understand the pattern using a small sample and reasoning, you can get this question right in under two minutes.

Re: If, for all positive integer values of n, P(n) is defined as [#permalink]
26 Apr 2013, 09:48

VeritasPrepRon wrote:

emmak wrote:

If, for all positive integer values of n, P(n) is defined as the sum of the smallest n prime numbers, then which of the following quantities are odd integers? I. P(10) II. P(P(10)) III. P(P(P(10)))

(A) I only (B) I and II only (C) I and III only (D) II and III only (E) I, II, and III

Express appreciation by pressing KUDOS button

This kind of question can give students fits. The key is to figure out what is being asked. The function P is summing up the first N prime numbers, so for example P(3) = 2 + 3 + 5. The total is 10. If I picked P(4), I'd get the same sum + 7, or 17.

Since the question hinges on whether the sum is even or odd, the only number that's unique in this circumstance is 2, as it is the only even prime number in an otherwise homogenous sea of odd numbers. Thus P(1) is even, P(2) is odd, P(3) is even again and P(4) is odd again. This is the pattern, so clearly P(10) will be 2 + nine odd numbers, so it will be odd. We can eliminate D.

P(P(10)) is where this starts getting interesting. You're doing the same test on a number we don't exactly know, but we know it must be odd. Since we know the pattern, the odd number will give us even. P(P(10)) will not be odd, eliminate B and E.

P(P(10))) will be the same function over a number we just calculated would be even. Hence it must be odd again. Eliminate A, the answer must be C.

Function questions are among the least understood questions on the GMAT, and this type of question can get people spending 3-4 minutes extrapolating numbers. If you understand the pattern using a small sample and reasoning, you can get this question right in under two minutes.

Hope this helps! -Ron

Ah that makes sense... took me a while.

I. Even + 9 odds = odd. II. Even + (odd * (odd - 1)) = even III. Even + (odd * (even - 1)) = odd

Re: If, for all positive integer values of n, P(n) is defined as [#permalink]
26 Feb 2014, 06:35

1

This post received KUDOS

Nice question +1. For this I would identify two cases: First we know that the only even number is 2. Therefore, if the number of prime integers that is n is even then the sum is odd, while if n is odd the sum is even.

In I we have that n is even therefore sum is odd. TRUE.

In II we have that the sum is odd so if we take that n is odd then the sum again will be even. FALSE.

In III, we get that the sum of n=10 is odd. Now the sum of odd is even and again the sum of even is odd. So III is TRUE as well.

Re: If, for all positive integer values of n, P(n) is defined as [#permalink]
26 Apr 2015, 22:03

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email. _________________

Harvard asks you to write a post interview reflection (PIR) within 24 hours of your interview. Many have said that there is little you can do in this...