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

It is currently 15 Oct 2018, 03:43

Close

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
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.

Close

Request Expert Reply

Confirm Cancel

The sequence A is defined by the following relationship:

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Intern
Intern
avatar
B
Joined: 09 Sep 2016
Posts: 35
Location: Georgia
Concentration: Finance, International Business
GPA: 3.75
WE: Analyst (Investment Banking)
The sequence A is defined by the following relationship:  [#permalink]

Show Tags

New post 23 Mar 2017, 10:18
5
4
00:00
A
B
C
D
E

Difficulty:

  65% (hard)

Question Stats:

65% (03:12) correct 35% (02:48) wrong based on 116 sessions

HideShow timer Statistics

The sequence A is defined by the following relationship: \(A_n\)= \(A_{n-1}\) + \((-1)^{n+1}\)\((n)^2\)for all integer values \(n >1\). If \(A_1\) \(=1\) , what is \(A_{15}\) - \(A_{13}\) ?

A) 14
B) 29
C) 169
D) 196
E) 421

Hit kudos if you liked the question
Most Helpful Community Reply
Senior Manager
Senior Manager
avatar
B
Joined: 13 Oct 2016
Posts: 367
GPA: 3.98
Re: The sequence A is defined by the following relationship:  [#permalink]

Show Tags

New post 23 Mar 2017, 10:59
6
4
giobas wrote:
The sequence A is defined by the following relationship: \(A_n\)= \(A_{n-1}\) + \((-1)^{n+1}\)\((n)^2\)for all integer values \(n >1\). If \(A_1\) \(=1\) , what is \(A_{15}\) - \(A_{13}\) ?

A) 14
B) 29
C) 169
D) 196
E) 421

Hit kudos if you liked the question


Hi

\(A_n - A_{n-1} =\) \((-1)^{n+1}\)\((n)^2\)

\(A_{15} - A_{14} = (-1)^{16} * 225 = 225\)

\(A_{14} - A_{13} = (-1)^{15}*196 = -196\)

\(A_{15} - A_{14} + A_{14} - A_{13} = A_{15} - A_{13} = 225 - 196 = 29\)

Answer B
General Discussion
Manager
Manager
avatar
B
Joined: 08 Sep 2016
Posts: 118
The sequence A is defined by the following relationship:  [#permalink]

Show Tags

New post 03 Apr 2018, 15:19
1
Brutal problem but I was able to see the pattern after over 2 minutes of trying it out.

A1 = 1
A2 = -3
A3 = 6
A4 = -10
A5 = 15

There's a pattern here. The odd sequence number multiplied by the progression step equal value (i'm not sure if that makes sense haha).

Example:
A1 = 1*1= 1
A3 = 3*2 = 6
A5 = 5*3= 15
....
A13 = 13*7 = 91
A15 = 15*8 = 120

A15 - A13 = 120-91 = 29.

Answer b
GMAT Club Bot
The sequence A is defined by the following relationship: &nbs [#permalink] 03 Apr 2018, 15:19
Display posts from previous: Sort by

The sequence A is defined by the following relationship:

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


Copyright

GMAT Club MBA Forum Home| About| Terms and Conditions and Privacy Policy| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.