NEW HERE? LEARN MORE
closeclose
Last visit was: 26 Apr 2024, 06:39 It is currently 26 Apr 2024, 06:39
Decision Tracker
My Rewards
New posts
New comers' posts

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.
Go to My Error Log Learn more
Close
Request Expert Reply
Confirm Cancel

If the 3rd term of sequence A is 15, what is the 2nd term?

SORT BY:
Date
Kudos
Tags:
Find Similar Topics 
Show Tags
Hide Tags
User avatar
L
EMPOWERgmatRichC
GMAT Club Legend
GMAT Club Legend
Joined: 19 Dec 2014
Status:GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Posts: 21846
Own Kudos [?]: 11668 [2]
Given Kudos: 450
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: Q170 V170
Send PM
If the 3rd term of sequence A is 15, what is the 2nd term? [#permalink] New post   Updated on: 04 Oct 2019, 16:40
2
Bookmarks
Expert Reply
00:00
A
B
C
D
E

Difficulty:

35% (medium)

Question Stats:

70% (01:30) correct 30% (01:27) wrong based on 142 sessions
Hide Show timer Statistics
EMPOWERgmat DS Series:
Pack 2, Question 1

If the 3rd term of sequence A is 15 and all of the terms in the sequence are positive, then what is the 2nd term?

1) The 1st term of A is 5.
2) Each term of A after the 1st term is y times the preceding term.


48 Hour Window To Win An $85 EMPOWERgmat Tuition Credit (1 Month Free!)
Share your explanation! The GMAT Club member with the most verified Kudos in total on the 5 question DS Block 2 question pack will win an $85 EMPOWERgmat tuition credit, which will entitle the winner to a full month of complete access to the EMPOWERgmat system. Even if you're not sure about your answer or your rationale, share your explanation to help boost your learning and earn a chance to win.

To be eligible, your explanation must be submitted within the 48 hour window after this post was created and should explain your reasoning why the answer you chose is correct

The OA and official explanation will be held until the 48 hour window has lapsed.
ShowHide Answer
Official Answer
C

Originally posted by EMPOWERgmatRichC on 01 Oct 2019, 21:06.
Last edited by EMPOWERgmatRichC on 04 Oct 2019, 16:40, edited 1 time in total.
User avatar
D
minustark
Senior Manager
Senior Manager
Joined: 14 Jul 2019
Status:Student
Posts: 478
Own Kudos [?]: 369 [2]
Given Kudos: 52
Location: United States
Concentration: Accounting, Finance
Schools: Zicklin Baruch "22
GMAT 1: 650 Q45 V35
GPA: 3.9
WE:Education (Accounting)
Send PM
Reviews Badge
Re: If the 3rd term of sequence A is 15, what is the 2nd term? [#permalink] New post   03 Oct 2019, 16:13
2
Kudos
From Statement 1, we get the 1st term of the sequence, 5. But, from this we cannot infer about the 2nd term. It can be of any value. NOT SUFFICIENT.
Statement 2 tells us each term of the sequence is y times the preceding term. But it doesn't specify the value of y, without which we cannot get the value of any other term. NOT SUFFICIENT.

Together, 1st term, A= 5
2nd term, A*y=5y
3rd term, A* y^2 = 5y^2 =15 , or y^2= 10,

So y will be the positive root of 10 as 3rd term is greater than 1st term. From this we will get the 2nd term. SUFFICIENT.

Answer is C.
User avatar
L
EMPOWERgmatRichC
GMAT Club Legend
GMAT Club Legend
Joined: 19 Dec 2014
Status:GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Posts: 21846
Own Kudos [?]: 11668 [1]
Given Kudos: 450
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: Q170 V170
Send PM
If the 3rd term of sequence A is 15, what is the 2nd term? [#permalink] New post   Updated on: 07 Oct 2019, 19:31
1
Kudos
Expert Reply
OFFICIAL EXPLANATION

Hi All,

We're told that all of the terms in a sequence are positive and the 3rd term of sequence A is 15. We're asked for the 2nd term of the sequence.

1) The 1st term of A is 5.

Knowing 2 terms of the sequence is not enough to define how the sequence 'works' - or any of the other terms in the sequence. It's certainly possible that the sequence is Arithmetic and 'increases by 5' from term to term... meaning that the first three terms would be 5, 10 and 15.... and the answer to the question would be 10.

However, it's also possible that the sequence is Geometric and each term increases by some constant product (such as √3)... meaning that the first three terms would be 5, 5√3 and 15... and the answer to the question would be 5√3.
Fact 1 is INSUFFICIENT

2) Each term of A after the 1st term is y times the preceding term.

Fact 2 tells us how the sequence works, but without the first term in the sequence, we cannot determine the second term in the sequence.
Fact 2 is INSUFFICIENT

Combined, we know...
-The 1st term of A is 5.
-Each term of A after the 1st term is y times the preceding term.

With the information in both Facts, we know that the first term is 5, the third term is 15 and each term increases by some constant product. The only way for that sequence to exist is if y = √3... meaning that the first three terms are 5, 5√3 and 15... and the answer to the question is 5√3.

Combined, SUFFICIENT

Final Answer:
Show Spoiler
C


GMAT assassins aren't born, they're made,
Rich

Originally posted by EMPOWERgmatRichC on 04 Oct 2019, 16:39.
Last edited by EMPOWERgmatRichC on 07 Oct 2019, 19:31, edited 1 time in total.
avatar
B
colinlin1
Intern
Intern
Joined: 05 Mar 2018
Posts: 16
Own Kudos [?]: 5 [1]
Given Kudos: 19
Send PM
Re: If the 3rd term of sequence A is 15, what is the 2nd term? [#permalink] New post   04 Oct 2019, 23:02
1
Kudos
minustark wrote:
From Statement 1, we get the 1st term of the sequence, 5. But, from this we cannot infer about the 2nd term. It can be of any value. NOT SUFFICIENT.
Statement 2 tells us each term of the sequence is y times the preceding term. But it doesn't specify the value of y, without which we cannot get the value of any other term. NOT SUFFICIENT.

Together, 1st term, A= 5
2nd term, A*y=5y
3rd term, A* y^2 = 5y^2 =15 , or y^2= 10,

So y will be the positive root of 10 as 3rd term is greater than 1st term. From this we will get the 2nd term. SUFFICIENT.

Answer is C.


Good logic, but Y^2 should be 3 not 10, y is the square root of 3
User avatar
L
EMPOWERgmatRichC
GMAT Club Legend
GMAT Club Legend
Joined: 19 Dec 2014
Status:GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Posts: 21846
Own Kudos [?]: 11668 [0]
Given Kudos: 450
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: Q170 V170
Send PM
Re: If the 3rd term of sequence A is 15, what is the 2nd term? [#permalink] New post   07 Oct 2019, 19:32
Expert Reply
Hi colinlin1,

Thanks for catching that typo; I've corrected it in my explanation.

GMAT assassins aren't born, they're made,
Rich
avatar
B
ankitprad
Intern
Intern
Joined: 18 Jul 2019
Posts: 36
Own Kudos [?]: 35 [1]
Given Kudos: 128
Send PM
Re: If the 3rd term of sequence A is 15, what is the 2nd term? [#permalink] New post   14 Oct 2019, 12:17
1
Kudos
EMPOWERgmatRichC wrote:
OFFICIAL EXPLANATION

Hi All,

We're told that all of the terms in a sequence are positive and the 3rd term of sequence A is 15. We're asked for the 2nd term of the sequence.

1) The 1st term of A is 5.

Knowing 2 terms of the sequence is not enough to define how the sequence 'works' - or any of the other terms in the sequence. It's certainly possible that the sequence is Arithmetic and 'increases by 5' from term to term... meaning that the first three terms would be 5, 10 and 15.... and the answer to the question would be 10.

However, it's also possible that the sequence is Geometric and each term increases by some constant product (such as √3)... meaning that the first three terms would be 5, 5√3 and 15... and the answer to the question would be 5√3.
Fact 1 is INSUFFICIENT



2) Each term of A after the 1st term is y times the preceding term.

Fact 2 tells us how the sequence works, but without the first term in the sequence, we cannot determine the second term in the sequence.
Fact 2 is INSUFFICIENT

Combined, we know...
-The 1st term of A is 5.
-Each term of A after the 1st term is y times the preceding term.

With the information in both Facts, we know that the first term is 5, the third term is 15 and each term increases by some constant product. The only way for that sequence to exist is if y = √3... meaning that the first three terms are 5, 5√3 and 15... and the answer to the question is 5√3.

Combined, SUFFICIENT

Final Answer:
Show Spoiler
C


GMAT assassins aren't born, they're made,
Rich



Hi, from both, Y^2 =3==> Y= +/- √3, shouldn't the answer still be E?? or should I ignore the -ve sign because its an AP.?
User avatar
L
EMPOWERgmatRichC
GMAT Club Legend
GMAT Club Legend
Joined: 19 Dec 2014
Status:GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Posts: 21846
Own Kudos [?]: 11668 [0]
Given Kudos: 450
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: Q170 V170
Send PM
Re: If the 3rd term of sequence A is 15, what is the 2nd term? [#permalink] New post   14 Oct 2019, 16:37
Expert Reply
Hi ankitprad,

You pose an important question - and under certain situations, you would have to consider negative values. However, the prompt tells us that all of the terms in the sequence are POSITIVE... and if you multiplied the first, positive term by a negative number, then the second term would be NEGATIVE. That does not fit the 'restrictions' given by the prompt, so it's not a possibility.

GMAT assassins aren't born, they're made,
Rich
User avatar
bumpbot
Non-Human User
Joined: 09 Sep 2013
Posts: 32684
Own Kudos [?]: 822 [0]
Given Kudos: 0
Send PM
Re: If the 3rd term of sequence A is 15, what is the 2nd term? [#permalink] New post   15 May 2023, 01:37
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 Club Bot
gmatclubot
Re: If the 3rd term of sequence A is 15, what is the 2nd term? [#permalink]
15 May 2023, 01:37
Moderator:
Bunuel
Math Expert
92933 posts

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne
Main navigation
GMAT Resources
Partners
MBA Resources
www.gmac.com|www.mba.com | | GMAT Club Rules | Terms and Conditions