Check GMAT Club Decision Tracker for the Latest School Decision Releases https://gmatclub.com/AppTrack

 It is currently 26 May 2017, 23:01

### 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

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# The second, the first and the third term of an AP whose comm

Author Message
TAGS:

### Hide Tags

Manager
Status: Taking heavily leveraged but calculated risks at all times
Joined: 04 Apr 2010
Posts: 183
Concentration: Entrepreneurship, Finance
Schools: HBS '15, Stanford '15
GMAT Date: 01-31-2012
Followers: 1

Kudos [?]: 72 [0], given: 12

The second, the first and the third term of an AP whose comm [#permalink]

### Show Tags

08 Dec 2011, 08:15
9
This post was
BOOKMARKED
00:00

Difficulty:

65% (hard)

Question Stats:

58% (03:07) correct 42% (01:43) wrong based on 146 sessions

### HideShow timer Statistics

The second, the first and the third term of an AP whose common difference is non zero but lesser than 200, form a GP in that order. What is the common ration of that GP?

A. 1
B. -1
C. 2
D. -2
E. |1|
[Reveal] Spoiler: OA

Last edited by Bunuel on 12 Jul 2013, 13:01, edited 1 time in total.
Renamed the topic and edited the question.
Manager
Joined: 24 Oct 2011
Posts: 94
Location: India
GMAT Date: 11-29-2011
GPA: 3.5
WE: Web Development (Computer Software)
Followers: 1

Kudos [?]: 16 [1] , given: 27

### Show Tags

08 Dec 2011, 09:44
1
KUDOS
its D

think A.P to be a-d,a,a+d.
G.P will be a,a-d,a+d

which means (a-d)^2 = a^2 + ad
that means d=3
and G.P is -1,2,-4 and A.P is 2,-1,-4. so G.P common ratio is -2 .....
Manager
Status: Taking heavily leveraged but calculated risks at all times
Joined: 04 Apr 2010
Posts: 183
Concentration: Entrepreneurship, Finance
Schools: HBS '15, Stanford '15
GMAT Date: 01-31-2012
Followers: 1

Kudos [?]: 72 [0], given: 12

### Show Tags

08 Dec 2011, 10:00
avenkatesh007 wrote:
its D

which means (a-d)^2 = a^2 + ad
that means d=3

Can you please elaborate on how you solved the quad with two unknowns variables.
Manager
Joined: 24 Oct 2011
Posts: 94
Location: India
GMAT Date: 11-29-2011
GPA: 3.5
WE: Web Development (Computer Software)
Followers: 1

Kudos [?]: 16 [4] , given: 27

### Show Tags

08 Dec 2011, 10:13
4
KUDOS
d=3a
here I assumed 'a' to be 1 coz in G.P ratio will be a+d:a kind of.so it wont matter what 'a' is.......else u can substitute direct values interms of 'a'.
Senior Manager
Joined: 12 Oct 2011
Posts: 265
Followers: 0

Kudos [?]: 50 [0], given: 110

### Show Tags

03 Jan 2012, 04:43
I am getting the ratio as -1/2. Can someone please explain how it is -2?
_________________

Consider KUDOS if you feel the effort's worth it

Intern
Joined: 28 Feb 2011
Posts: 35
Followers: 0

Kudos [?]: 7 [0], given: 1

### Show Tags

03 Jan 2012, 15:02
avenkatesh007 wrote:
its D

think A.P to be a-d,a,a+d.
G.P will be a,a-d,a+d

which means (a-d)^2 = a^2 + ad
that means d=3
and G.P is -1,2,-4 and A.P is 2,-1,-4. so G.P common ratio is -2 .....

Hi,

Can you please explain how did u get:

Thanks,
Anu
Manager
Status: MBA Aspirant
Joined: 12 Jun 2010
Posts: 176
Location: India
WE: Information Technology (Investment Banking)
Followers: 3

Kudos [?]: 89 [0], given: 1

### Show Tags

04 Jan 2012, 21:49
anuu wrote:
avenkatesh007 wrote:
its D

think A.P to be a-d,a,a+d.
G.P will be a,a-d,a+d

which means (a-d)^2 = a^2 + ad
that means d=3
and G.P is -1,2,-4 and A.P is 2,-1,-4. so G.P common ratio is -2 .....

Hi,

Can you please explain how did u get:

Thanks,
Anu

for GP we use b^2=ac

so using that (a-d)^2 = a(a+d)

by solving this we get d=3a

but the common difference is comming to be -1/2
can anyone please comment on this.
Senior Manager
Joined: 12 Oct 2011
Posts: 265
Followers: 0

Kudos [?]: 50 [0], given: 110

### Show Tags

05 Jan 2012, 21:23
subhajeet, I have cited the same problem above. Even I am getting the ratio as -1/2. Wonder if we are missing something vital here.
_________________

Consider KUDOS if you feel the effort's worth it

Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 7377
Location: Pune, India
Followers: 2288

Kudos [?]: 15128 [4] , given: 224

### Show Tags

06 Jan 2012, 04:15
4
KUDOS
Expert's post
9
This post was
BOOKMARKED
Anasthaesium wrote:
The second, the first and the third term of an AP whose common difference is non zero but lesser than 200, form a GP in that order. What is the common ration of that GP?

a)1
b)-1
c)2
d)-2
e)|1|

Detailed algebraic explanation:

Let the 3 terms of the AP be (a-d), a and (a+d)
Terms of the GP: a, (a-d), (a+d) in that order.
In a GP, terms next to each other have the same ratio.
So, $$\frac{(a-d)}{a} = \frac{(a+d)}{(a-d)}$$

$$(a-d)^2 = a(a+d)$$

$$d^2 - 2ad = ad$$

$$d^2 - 3ad = 0$$

$$d(d - 3a) = 0$$

We know that d is not 0 from the question. So d = 3a

Common ratio $$= \frac{(a-d)}{a} = \frac{(a - 3a)}{a} = -2$$
_________________

Karishma
Veritas Prep | GMAT Instructor
My Blog

Get started with Veritas Prep GMAT On Demand for $199 Veritas Prep Reviews Veritas Prep GMAT Instructor Joined: 16 Oct 2010 Posts: 7377 Location: Pune, India Followers: 2288 Kudos [?]: 15128 [1] , given: 224 Re: Progessions Ap/Gp/both?? [#permalink] ### Show Tags 06 Jan 2012, 04:17 1 This post received KUDOS Expert's post siddharthmuzumdar wrote: subhajeet, I have cited the same problem above. Even I am getting the ratio as -1/2. Wonder if we are missing something vital here. You probably got d = 3a but after that, substituted d in a/(a-d) as one would naturally since (a-d) is smaller than a. But, the terms in the GP are a, (a-d), (a+d) in that order. So the common ratio is (a-d)/a or (a+d)/(a-d) _________________ Karishma Veritas Prep | GMAT Instructor My Blog Get started with Veritas Prep GMAT On Demand for$199

Veritas Prep Reviews

Manager
Status: MBA Aspirant
Joined: 12 Jun 2010
Posts: 176
Location: India
WE: Information Technology (Investment Banking)
Followers: 3

Kudos [?]: 89 [0], given: 1

### Show Tags

06 Jan 2012, 04:56
VeritasPrepKarishma wrote:
siddharthmuzumdar wrote:
subhajeet, I have cited the same problem above. Even I am getting the ratio as -1/2. Wonder if we are missing something vital here.

You probably got d = 3a but after that, substituted d in a/(a-d) as one would naturally since (a-d) is smaller than a. But, the terms in the GP are a, (a-d), (a+d) in that order. So the common ratio is (a-d)/a or (a+d)/(a-d)

Karishma: U got me right. I was indeed making the same mistake as you have mentioned here. Thanks for the reply.
Senior Manager
Joined: 12 Oct 2011
Posts: 265
Followers: 0

Kudos [?]: 50 [0], given: 110

### Show Tags

07 Jan 2012, 02:32
VeritasPrepKarishma wrote:
siddharthmuzumdar wrote:
subhajeet, I have cited the same problem above. Even I am getting the ratio as -1/2. Wonder if we are missing something vital here.

You probably got d = 3a but after that, substituted d in a/(a-d) as one would naturally since (a-d) is smaller than a. But, the terms in the GP are a, (a-d), (a+d) in that order. So the common ratio is (a-d)/a or (a+d)/(a-d)

Grrr....I am just cursing myself for such silly mistakes.
Thanks a ton for pointing it out.
_________________

Consider KUDOS if you feel the effort's worth it

GMAT Club Legend
Joined: 09 Sep 2013
Posts: 15474
Followers: 649

Kudos [?]: 209 [0], given: 0

Re: The second, the first and the third term of an AP whose comm [#permalink]

### Show Tags

25 Oct 2014, 00:17
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.
_________________
Manager
Joined: 18 Jul 2013
Posts: 52
Followers: 0

Kudos [?]: 5 [0], given: 151

The second, the first and the third term of an AP whose comm [#permalink]

### Show Tags

18 Nov 2014, 10:43
Hi Karishma,

I am bit confuse with this AP and GP, is it Arithmetic progression and geometric progression. And how do we decide this sequence of a,a-d, a+d.
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 7377
Location: Pune, India
Followers: 2288

Kudos [?]: 15128 [1] , given: 224

Re: The second, the first and the third term of an AP whose comm [#permalink]

### Show Tags

18 Nov 2014, 23:37
1
KUDOS
Expert's post
2
This post was
BOOKMARKED
taleesh wrote:
Hi Karishma,

I am bit confuse with this AP and GP, is it Arithmetic progression and geometric progression. And how do we decide this sequence of a,a-d, a+d.

Yes, AP is Arithmetic Progression, GP is Geometric Progression.

The second first and third terms of an AP form a GP when put in that order.

How do we express the terms of AP? Three terms can be expressed as
a-d, a, a+d (with d as the common difference)

When you put them in this order: second, first and third
a, a-d, a+d - this is a GP

A GP has common ratio so (a-d)/a = (a+d)/(a-d) = Common Ratio

More on AP and GP:

http://www.veritasprep.com/blog/2012/03 ... gressions/
http://www.veritasprep.com/blog/2012/03 ... gressions/
http://www.veritasprep.com/blog/2012/04 ... gressions/
_________________

Karishma
Veritas Prep | GMAT Instructor
My Blog

Get started with Veritas Prep GMAT On Demand for $199 Veritas Prep Reviews GMAT Club Legend Joined: 09 Sep 2013 Posts: 15474 Followers: 649 Kudos [?]: 209 [0], given: 0 Re: The second, the first and the third term of an AP whose comm [#permalink] ### Show Tags 13 Apr 2016, 08:11 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. _________________ Manager Joined: 23 Jan 2016 Posts: 185 Followers: 1 Kudos [?]: 17 [0], given: 491 Re: The second, the first and the third term of an AP whose comm [#permalink] ### Show Tags 27 Apr 2016, 09:33 this does not look like a GMAT question. Please let me know if im wrong. Veritas Prep GMAT Instructor Joined: 16 Oct 2010 Posts: 7377 Location: Pune, India Followers: 2288 Kudos [?]: 15128 [0], given: 224 Re: The second, the first and the third term of an AP whose comm [#permalink] ### Show Tags 27 Apr 2016, 19:46 abypatra wrote: this does not look like a GMAT question. Please let me know if im wrong. The concept could easily be tested this way in GMAT though the wording of the question would be much more explicit. _________________ Karishma Veritas Prep | GMAT Instructor My Blog Get started with Veritas Prep GMAT On Demand for$199

Veritas Prep Reviews

Re: The second, the first and the third term of an AP whose comm   [#permalink] 27 Apr 2016, 19:46
Similar topics Replies Last post
Similar
Topics:
The first term in a sequence is 1 and the second term is 5. From the 3 12 May 2016, 11:21
What is the difference between the fourth and third terms of the 2 30 Nov 2015, 04:25
9 The first term of a sequence is -2 and the second term is 2. Each 6 07 Mar 2017, 04:40
6 Find the sum of the first 15 terms of the series whose nth 6 27 Mar 2015, 05:24
25 If the first, third and thirteenth terms of an arithmetic 15 12 Aug 2016, 09:00
Display posts from previous: Sort by