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 500,000 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:

For the positive integers a, b, and k, a^k||b means that a^k [#permalink]

Show Tags

12 Dec 2012, 03:59

3

This post received KUDOS

9

This post was BOOKMARKED

00:00

A

B

C

D

E

Difficulty:

25% (medium)

Question Stats:

72% (02:19) correct
28% (01:30) wrong based on 995 sessions

HideShow timer Statistics

For the positive integers a, b, and k, a^k||b means that a^k is a divisor of b, but a^(k + 1) is not a divisor of b. If k is a positive integer and 2^k||72, then k is equal to

Re: For the positive integers a, b, and k, a^k||b means that a^k [#permalink]

Show Tags

12 Dec 2012, 04:02

2

This post received KUDOS

Expert's post

7

This post was BOOKMARKED

Walkabout wrote:

For the positive integers a, b, and k, a^k||b means that a^k is a divisor of b, but a^(k + 1) is not a divisor of b. If k is a positive integer and 2^k||72, then k is equal to

(A) 2 (B) 3 (C) 4 (D) 8 (E) 18

\(72=2^3*3^2\), so we have that 2^3 is a divisor of 72 and 2^4 is not. Thus 2^3||72, hence k=3.

Re: For the positive integers a, b, and k, a^k||b means that a^k [#permalink]

Show Tags

14 Dec 2012, 23:44

2

This post received KUDOS

Initially looking to the problem one may try to plugin the numbers one by one. Here, 2^2=4 is a divisor of 72 and 2^3=8 is also a divisor of 72. But, we have to choose only one answer. 72=2x2x2x3x3=2^3 *3^2 and it is given that 72/2^k = integer. Here, we can equate 2^3=2^k and hence k=3. But, in fact 2^2 is also a divisor of 72 hence 2 could also be the answer. But, since it is additionally given that k+1 is not a divisor i.e. 2 in this case does not satisfy the condition because 2+1=3 and 2^3 is a divisior of 72. where as 3 satisfies the condition i.e. 3+1= 4 turning into 2^4 which is not a divisor of 72. This is how only one answer choice is left which is equal to 3 = answer choice B.

Re: For the positive integers a, b, and k, a^k||b means that a^k [#permalink]

Show Tags

11 Sep 2014, 02:40

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. _________________

Re: For the positive integers a, b, and k, a^k||b means that a^k [#permalink]

Show Tags

11 Sep 2014, 11:29

1

This post received KUDOS

Walkabout wrote:

For the positive integers a, b, and k, a^k||b means that a^k is a divisor of b, but a^(k + 1) is not a divisor of b. If k is a positive integer and 2^k||72, then k is equal to

(A) 2 (B) 3 (C) 4 (D) 8 (E) 18

72 = 2*2*2*3*3

72/ 2^k = int ; 72/2^k+1 not integer

if k= 2 then divisible ,k=3 then also .. if K=3 then divisible , k=4 then not..

Re: For the positive integers a, b, and k, a^k||b means that a^k [#permalink]

Show Tags

28 Aug 2015, 21:28

Bunuel wrote:

Walkabout wrote:

For the positive integers a, b, and k, a^k||b means that a^k is a divisor of b, but a^(k + 1) is not a divisor of b. If k is a positive integer and 2^k||72, then k is equal to

(A) 2 (B) 3 (C) 4 (D) 8 (E) 18

\(72=2^3*3^2\), so we have that 2^3 is a divisor of 72 and 2^4 is not. Thus 2^3||72, hence k=3.

Answer: B.

Why is the answer not A? if k= 2 it is still a divisor of 72 _________________

Kindly support by giving Kudos, if my post helped you!

Re: For the positive integers a, b, and k, a^k||b means that a^k [#permalink]

Show Tags

29 Aug 2015, 02:16

Expert's post

1

This post was BOOKMARKED

harishbiyani8888 wrote:

Bunuel wrote:

Walkabout wrote:

For the positive integers a, b, and k, a^k||b means that a^k is a divisor of b, but a^(k + 1) is not a divisor of b. If k is a positive integer and 2^k||72, then k is equal to

(A) 2 (B) 3 (C) 4 (D) 8 (E) 18

\(72=2^3*3^2\), so we have that 2^3 is a divisor of 72 and 2^4 is not. Thus 2^3||72, hence k=3.

Answer: B.

Why is the answer not A? if k= 2 it is still a divisor of 72

We need such k that 2^k IS a divisor of 72 but 2^(k+1) is NOT. k cannot be 2 because 2^(2+1) IS a divisor of 72. _________________

Re: For the positive integers a, b, and k, a^k||b means that a^k [#permalink]

Show Tags

18 May 2016, 12:30

Walkabout wrote:

For the positive integers a, b, and k, a^k||b means that a^k is a divisor of b, but a^(k + 1) is not a divisor of b. If k is a positive integer and 2^k||72, then k is equal to

(A) 2 (B) 3 (C) 4 (D) 8 (E) 18

Solution:

This is called a "defined function" problem. The parallel lines mean intrinsically nothing, except to establish a relationship between a^k and b.We are given that a^k || b means:

1) b/a^k = integer

2) b/a^(k+1) ≠ integer

Next we are given specific numbers 2^k || 72, and we must use the pattern to determine k, using a = 2 and b = 72; thus, we know:

72/2^k = integer AND 72/2^(k+1) ≠ integer

In order for 72/2^k = integer AND 72/2^(k+1) ≠ integer to be true, k must equal 3. If have trouble seeing how this works, we can plug 3 back in to prove it.

When k = 3, we know:

1) 72/2^3 = 72/8 = 9, which IS an integer.

AND

2) 72/2^(3+1) = 72/2^4 = 72/16 = 4 1/2, which is NOT an integer.

The answer is B. _________________

Jeffrey Miller Jeffrey Miller Head of GMAT Instruction

gmatclubot

Re: For the positive integers a, b, and k, a^k||b means that a^k
[#permalink]
18 May 2016, 12:30

http://blog.ryandumlao.com/wp-content/uploads/2016/05/IMG_20130807_232118.jpg The GMAT is the biggest point of worry for most aspiring applicants, and with good reason. It’s another standardized test when most of us...

I recently returned from attending the London Business School Admits Weekend held last week. Let me just say upfront - for those who are planning to apply for the...