GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 19 Aug 2019, 16:30

### 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

# If n = 3^8 - 2^8, which of the following is NOT a factor of

Author Message
TAGS:

### Hide Tags

Manager
Joined: 24 Sep 2018
Posts: 100
Location: India
Re: If n = 3^8 - 2^8, which of the following is NOT a factor of  [#permalink]

### Show Tags

23 Jul 2019, 03:09
If n = 3^8 - 2^8, which of the following is NOT a factor of n?

(A) 97
(B) 65
(C) 35
(D) 13
(E) 5

_________________
Thanks,
Bijaya

If this post is helpful for you please press the kudos button
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 9540
Location: Pune, India
Re: If n = 3^8 - 2^8, which of the following is NOT a factor of  [#permalink]

### Show Tags

23 Jul 2019, 03:36
BijayKru wrote:
If n = 3^8 - 2^8, which of the following is NOT a factor of n?

(A) 97
(B) 65
(C) 35
(D) 13
(E) 5

$$n = 3^8 - 2^8$$
$$= (3^4 + 2^4)*(3^4 - 2^4)$$
$$= (3^4 + 2^4)(3^2 + 2^2)(3^2 - 2^2)$$
$$= (3^4 + 2^4)(3^2 + 2^2)(3 + 2)(3 - 2)$$
$$= 97*13*5*1$$
35 is not a factor of n since there is no 7 in n.

_________________
Karishma
Veritas Prep GMAT Instructor

Manager
Joined: 11 Dec 2018
Posts: 50
Re: If n = 3^8 - 2^8, which of the following is NOT a factor of  [#permalink]

### Show Tags

23 Jul 2019, 03:56
Easiest way is to convert the equation to the formula a^2-b^2

3^8-2^8
=9^4-4^4
=81^2-16^2
=(81-16)(81+16)
=65*97

Therefore, only option C that is 7*5 remains because 7 is neither a factor of 97 nor of 65.

Kudos for some appreciation please, if you like my explanation. I also welcome Critical analysis of my post that will help me reach 700+ level.

Posted from my mobile device
Manager
Joined: 11 Dec 2018
Posts: 50
Re: If n = 3^8 - 2^8, which of the following is NOT a factor of  [#permalink]

### Show Tags

23 Jul 2019, 03:56
Easiest way is to convert the equation to the formula a^2-b^2

3^8-2^8
=9^4-4^4
=81^2-16^2
=(81-16)(81+16)
=65*97

Therefore, only option C that is 7*5 remains because 7 is neither a factor of 97 nor of 65.

Kudos for some appreciation please, if you like my explanation. I also welcome Critical analysis of my post that will help me reach 700+ level.

Posted from my mobile device
Re: If n = 3^8 - 2^8, which of the following is NOT a factor of   [#permalink] 23 Jul 2019, 03:56

Go to page   Previous    1   2   [ 24 posts ]

Display posts from previous: Sort by