Find all School-related info fast with the new School-Specific MBA Forum

It is currently 29 Apr 2016, 06:09
GMAT Club Tests

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.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

5 and 15 are the first two terms in a geometric sequence.

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Director
Director
avatar
Joined: 29 Nov 2012
Posts: 901
Followers: 12

Kudos [?]: 774 [0], given: 543

5 and 15 are the first two terms in a geometric sequence. [#permalink]

Show Tags

New post 22 Jun 2013, 05:47
1
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

  45% (medium)

Question Stats:

62% (02:06) correct 38% (01:06) wrong based on 119 sessions

HideShow timer Statictics

5 and 15 are the first two terms in a geometric sequence. What is the arithmetic difference between the 11th term and the 13th term?

A. 3*5^2
B. 5* 3^13 - 5 * 3^11
C. 5^13
D. 40 * 3^10
E. 3^12 - 3^10

[Reveal] Spoiler:
Question regarding arithmetic difference is a - b / 2? or only a - b?
[Reveal] Spoiler: OA

_________________

Click +1 Kudos if my post helped...

Amazing Free video explanation for all Quant questions from OG 13 and much more http://www.gmatquantum.com/og13th/

GMAT Prep software What if scenarios gmat-prep-software-analysis-and-what-if-scenarios-146146.html

1 KUDOS received
Manager
Manager
User avatar
Status: *Lost and found*
Joined: 25 Feb 2013
Posts: 123
Location: India
Concentration: General Management, Technology
GMAT 1: 640 Q42 V37
GPA: 3.5
WE: Web Development (Computer Software)
Followers: 17

Kudos [?]: 95 [1] , given: 14

GMAT ToolKit User
Re: 5 and 15 are the first two terms in a geometric sequence. [#permalink]

Show Tags

New post 22 Jun 2013, 08:02
1
This post received
KUDOS
fozzzy wrote:
5 and 15 are the first two terms in a geometric sequence. What is the arithmetic difference between the 11th term and the 13th term?

a 3*5^2
b 5* 3^13 - 5 * 3^11
c 5^13
d 40 * 3^10
e 3^12 - 3^10

[Reveal] Spoiler:
Question regarding arithmetic difference is a - b / 2? or only a - b?


I think the answer choice should be 40 * 3^11. Please do check the source and correct me if I am wrong! Also, the fact that we are calculating the difference of the 13th and the 11th term since this is an increasing GP!

The first term or the a0 = 5 and a1 = 15. For geometric progression, a1 = r * a0 where r is the common term.
Hence, r comes out to be 3.

\(a13 - a11 = a0 * (r^13 - r^11) = 5 * (3^13 - 3^11) = 5 * 3^11 * (9-1) = 40 * 3^11\)

Hence, 40 * 3^11 should be the answer.

Regards,
Arpan
_________________

Feed me some KUDOS! :) :) *always hungry*

My Thread : Recommendation Letters

1 KUDOS received
Director
Director
avatar
Joined: 29 Nov 2012
Posts: 901
Followers: 12

Kudos [?]: 774 [1] , given: 543

Re: 5 and 15 are the first two terms in a geometric sequence. [#permalink]

Show Tags

New post 22 Jun 2013, 08:07
1
This post received
KUDOS
The formula for GP is \(A1*[r ^{(n-1)}]\)

so for 11th term it will be 10 and for 13th term it will be 12

sequences-progressions-101891.html
_________________

Click +1 Kudos if my post helped...

Amazing Free video explanation for all Quant questions from OG 13 and much more http://www.gmatquantum.com/og13th/

GMAT Prep software What if scenarios gmat-prep-software-analysis-and-what-if-scenarios-146146.html

Manager
Manager
User avatar
Status: *Lost and found*
Joined: 25 Feb 2013
Posts: 123
Location: India
Concentration: General Management, Technology
GMAT 1: 640 Q42 V37
GPA: 3.5
WE: Web Development (Computer Software)
Followers: 17

Kudos [?]: 95 [0], given: 14

GMAT ToolKit User
Re: 5 and 15 are the first two terms in a geometric sequence. [#permalink]

Show Tags

New post 22 Jun 2013, 08:16
fozzzy wrote:
The formula for GP is \(A1*[r ^{(n-1)}]\)

so for 11th term it will be 10 and for 13th term it will be 12

sequences-progressions-101891.html


My apologies! Since I started of the series with a0 I completely screwed up the counting! As you have mentioned, the 13th term will have the 12th power and the 11th term will have the 10th power! :) *precisely the difference between choice [B] and [D]*

And as you have mentioned, the arithmetic difference is the the simple difference of the two terms leading to the answer [D]!

Regards,
Arpan
_________________

Feed me some KUDOS! :) :) *always hungry*

My Thread : Recommendation Letters

Expert Post
Verbal Forum Moderator
Verbal Forum Moderator
User avatar
Joined: 10 Oct 2012
Posts: 630
Followers: 72

Kudos [?]: 919 [0], given: 136

Premium Member
Re: 5 and 15 are the first two terms in a geometric sequence. [#permalink]

Show Tags

New post 22 Jun 2013, 08:22
Expert's post
fozzzy wrote:
5 and 15 are the first two terms in a geometric sequence. What is the arithmetic difference between the 11th term and the 13th term?

a 3*5^2
b 5* 3^13 - 5 * 3^11
c 5^13
d 40 * 3^10
e 3^12 - 3^10

[Reveal] Spoiler:
Question regarding arithmetic difference is a - b / 2? or only a - b?


For a given Geometric Sequence, the \(n^{th}\) term is \(t_n = a*r^{n-1}\), where a is the first term and r is the common ratio. From the given problem, \(t_{11} = 5*3^{10}\) and \(t_{13} = 5*3^{12}\). Thus, the arithmetic difference is : \(5*3^{10}*(9-1)\) = \(40*3^{10}\).
_________________

All that is equal and not-Deep Dive In-equality

Hit and Trial for Integral Solutions

Expert Post
Math Expert
User avatar
Joined: 02 Sep 2009
Posts: 32530
Followers: 5620

Kudos [?]: 68191 [0], given: 9797

Re: 5 and 15 are the first two terms in a geometric sequence. [#permalink]

Show Tags

New post 22 Jun 2013, 13:16
Expert's post
fozzzy wrote:
5 and 15 are the first two terms in a geometric sequence. What is the arithmetic difference between the 11th term and the 13th term?

A. 3*5^2
B. 5* 3^13 - 5 * 3^11
C. 5^13
D. 40 * 3^10
E. 3^12 - 3^10

[Reveal] Spoiler:
Question regarding arithmetic difference is a - b / 2? or only a - b?


Similar questions to practice:
baker-s-dozen-128782-40.html#p1057517
if-the-sequence-x1-x2-x3-xn-is-such-that-x1-98536.html
_________________

New to the Math Forum?
Please read this: All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

GMAT Club Legend
GMAT Club Legend
User avatar
Joined: 09 Sep 2013
Posts: 9211
Followers: 453

Kudos [?]: 114 [0], given: 0

Premium Member
Re: 5 and 15 are the first two terms in a geometric sequence. [#permalink]

Show Tags

New post 24 Jan 2016, 21:27
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.
_________________

GMAT Books | GMAT Club Tests | Best Prices on GMAT Courses | GMAT Mobile App | Math Resources | Verbal Resources

Intern
Intern
avatar
Joined: 17 Sep 2015
Posts: 1
Location: India
Concentration: Finance, Strategy
Schools: UCLA EMBA"17
WE: Programming (Computer Software)
Followers: 0

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

GMAT ToolKit User
Re: 5 and 15 are the first two terms in a geometric sequence. [#permalink]

Show Tags

New post 24 Jan 2016, 22:24
Answer comes out to be 5 * (3^13 - 3^11) = 5 * 3^11*(3^2 - 1) = 5 * 3^11 * 8 = 40 * 3^11....

Only B depicts correct answer; but OA is "D" which says answer is 40 * 3^10 ...which is wrong...

Am I right guys?
Re: 5 and 15 are the first two terms in a geometric sequence.   [#permalink] 24 Jan 2016, 22:24
    Similar topics Author Replies Last post
Similar
Topics:
1 Experts publish their posts in the topic In a geometric sequence each term is found by multiplying the previous Bunuel 9 26 Jan 2015, 06:04
7 Experts publish their posts in the topic A geometric sequence is one in which the ratio of any term after the f Bunuel 4 11 Nov 2014, 09:16
4 Experts publish their posts in the topic A geometric sequence is a sequence in which each mau5 4 23 Apr 2013, 22:04
35 Experts publish their posts in the topic A sequence of numbers (geometric sequence) is given by the maglian 11 19 Jan 2013, 11:53
geometric sequence dreambeliever 4 17 Dec 2011, 08:01
Display posts from previous: Sort by

5 and 15 are the first two terms in a geometric sequence.

  Question banks Downloads My Bookmarks Reviews Important topics  


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

Powered by phpBB © phpBB Group and phpBB SEO

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®.