Last visit was: 26 Apr 2026, 04:36 It is currently 26 Apr 2026, 04:36
Home
Messages
Tests
Schools
Events
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
Back to Forum
Create Topic
555-605 (Medium)|   Algebra|   Exponents|      
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 26 Apr 2026
Posts: 109,832
Own Kudos:
811,335
 [9]
Given Kudos: 105,892
Products:
GMAT Club Tests Forum Quiz
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 109,832
Kudos: 811,335
 [9]
If y^(-2) + 2y^(-1) - 15 = 0, which of the following could be the valu 05 Jul 2018, 21:28
Kudos
Add Kudos
8
Bookmarks
Bookmark this Post
00:00
Start Timer
Pause Timer
Resume Timer
Show Answer
Hide
Show
History
C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!

Difficulty:

35% (medium)

Question Stats:

70% (01:44) correct 30% (02:10) wrong based on 260 sessions

History

Date
Time
Result
Not Attempted Yet
If \(y^{-2} + 2y^{-1} -15 = 0\), which of the following could be the value of y?


A. \(3\)

B. \(\frac{1}{5}\)

C. \(\frac{-1}{5}\)

D. \(\frac{-1}{3}\)

E. \(-5\)
ShowHide Answer
Official Answer
C
User avatar
PKN
User avatar
Joined: 01 Oct 2017
Last visit: 11 Oct 2025
Posts: 809
Own Kudos:
1,637
 [3]
Given Kudos: 41
Status:Learning stage
WE:Supply Chain Management (Energy)
Posts: 809
Kudos: 1,637
 [3]
If y^(-2) + 2y^(-1) - 15 = 0, which of the following could be the valu 05 Jul 2018, 21:38
3
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel
If \(y^{-2} + 2y^{-1} -15 = 0\), which of the following could be the value of y?


A. \(3\)

B. \(\frac{1}{5}\)

C. \(\frac{-1}{5}\)

D. \(\frac{-1}{3}\)

E. \(-5\)
Show more

Let \(y^{-1}=x\)

So, \(y^{-2} + 2y^{-1} -15 = 0\)
Or, \(x^2+2x-15=0\)
Or, x=-5 or x=3

1. x=-5, or, \(y^{-1}=-5\) or, \(y=\frac{-1}{5}\)
2. x=3,or, \(y^{-1}=3\) or, \(y=\frac{1}{3}\)

Among given options, correct answer is (C)
User avatar
PKN
User avatar
Joined: 01 Oct 2017
Last visit: 11 Oct 2025
Posts: 809
Own Kudos:
1,637
Given Kudos: 41
Status:Learning stage
WE:Supply Chain Management (Energy)
Posts: 809
Kudos: 1,637
If y^(-2) + 2y^(-1) - 15 = 0, which of the following could be the valu 08 Jul 2018, 05:26
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel
If \(y^{-2} + 2y^{-1} -15 = 0\), which of the following could be the value of y?


A. \(3\)

B. \(\frac{1}{5}\)

C \(\frac{-1}{5}\)

D. \(\frac{-1}{3}\)

E. \(-5\)
Show more

Let \(y^{-1}=x\)

So, \(y^{-2} + 2y^{-1} -15 = 0\)
Or, \(x^2+2x-15=0\)
Or, x=-5 or x=3

1. x=-5, or, \(y^{-1}=-5\) or, \(y=\frac{-1}{5}\)
2. x=3,or, \(y^{-1}=3\) or, \(y=\frac{1}{3}\)

Among given options, correct answer is (C)[/quote]
P.S:- Already discussed .
https://gmatclub.com/forum/if-y-2-2y-1- ... 69804.html
User avatar
Seryozha
User avatar
Joined: 04 Aug 2017
Last visit: 29 Nov 2019
Posts: 36
Own Kudos:
20
Given Kudos: 108
Status:No Progress without Struggle
Location: Armenia
GPA: 3.4
Posts: 36
Kudos: 20
If y^(-2) + 2y^(-1) - 15 = 0, which of the following could be the valu 09 Jul 2018, 03:44
Kudos
Add Kudos
Bookmarks
Bookmark this Post
PKN
Bunuel
If \(y^{-2} + 2y^{-1} -15 = 0\), which of the following could be the value of y?


A. \(3\)

B. \(\frac{1}{5}\)

C. \(\frac{-1}{5}\)

D. \(\frac{-1}{3}\)

E. \(-5\)

Let \(y^{-1}=x\)

So, \(y^{-2} + 2y^{-1} -15 = 0\)
Or, \(x^2+2x-15=0\)
Or, x=-5 or x=3

1. x=-5, or, \(y^{-1}=-5\) or, \(y=\frac{-1}{5}\)
2. x=3,or, \(y^{-1}=3\) or, \(y=\frac{1}{3}\)

Among given options, correct answer is (C)
Show more
Is there an alternative way to solve this problem?
User avatar
PKN
User avatar
Joined: 01 Oct 2017
Last visit: 11 Oct 2025
Posts: 809
Own Kudos:
1,637
Given Kudos: 41
Status:Learning stage
WE:Supply Chain Management (Energy)
Posts: 809
Kudos: 1,637
If y^(-2) + 2y^(-1) - 15 = 0, which of the following could be the valu 09 Jul 2018, 03:51
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Plugin answer choices and put in LHS of the given equation.The value of y for which the LHS becomes zero is the correct answer choice.

Posted from my mobile device
User avatar
Chethan92
User avatar
Joined: 18 Jul 2018
Last visit: 21 Apr 2022
Posts: 901
Own Kudos:
1,509
 [1]
Given Kudos: 95
Location: India
Concentration: Operations, General Management
Schools: IIMB EPGP'22 (M)
GMAT 1: 590 Q46 V25
GMAT 2: 690 Q49 V34
WE:Engineering (Energy)
Products:
My Reviews
Schools: IIMB EPGP'22 (M)
GMAT 2: 690 Q49 V34
Posts: 901
Kudos: 1,509
 [1]
If y^(-2) + 2y^(-1) - 15 = 0, which of the following could be the valu 22 Aug 2018, 06:54
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
\(y^{-2}\) can be written as \(\frac{1}{y^2}\)
Similarly \(y^{-1}\) can be written as \(\frac{1}{y}\)

Then the equation becomes \(\frac{1}{y^2}\) + 2\(\frac{1}{y}\) - 15 = 0.

Taking LCM, the equation becomes 1+2y-15\(y^2\) = 0.

Re-arranging gives 15\(y^2\)-2y-1 = 0.

15\(y^2\)-5y+3y-1 = 0.

5y(3y-1)+1(3y-1) = 0

Either y = \(\frac{-1}{3}\) or y = \(\frac{-1}{5}\).

Among the answer choices.

y = \(\frac{-1}{5}\)

C is the answer.
User avatar
bebs
User avatar
Joined: 18 Jun 2018
Last visit: 03 Dec 2021
Posts: 329
Own Kudos:
215
Given Kudos: 1,283
Concentration: Finance, Healthcare
Schools: Jones '22 (M$) McCombs '22 (WL) Kelley '22 (A$)
Schools: Jones '22 (M$) McCombs '22 (WL) Kelley '22 (A$)
Posts: 329
Kudos: 215
If y^(-2) + 2y^(-1) - 15 = 0, which of the following could be the valu 22 Aug 2018, 08:27
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Afc0892

Sure it is a typo (since you got the answer) but -1/3 is not a root, otherwise option D will be correct too. The roots are 1/3 and -1/5 (option C). I am also an arsenal fan. Up gunners!!!


Afc0892
\(y^{-2}\) can be written as \(\frac{1}{y^2}\)
Similarly \(y^{-1}\) can be written as \(\frac{1}{y}\)

Then the equation becomes \(\frac{1}{y^2}\) + 2\(\frac{1}{y}\) - 15 = 0.

Taking LCM, the equation becomes 1+2y-15\(y^2\) = 0.

Re-arranging gives 15\(y^2\)-2y-1 = 0.

15\(y^2\)-5y+3y-1 = 0.

5y(3y-1)+1(3y-1) = 0

Either y = \(\frac{-1}{3}\) or y = \(\frac{-1}{5}\).

Among the answer choices.

y = \(\frac{-1}{5}\)

C is the answer.
Show more
avatar
mandy0rhtdm
avatar
Joined: 14 Sep 2014
Last visit: 22 Oct 2022
Posts: 13
Own Kudos:
4
Given Kudos: 30
Location: India
Posts: 13
Kudos: 4
If y^(-2) + 2y^(-1) - 15 = 0, which of the following could be the valu 22 Aug 2018, 08:32
Kudos
Add Kudos
Bookmarks
Bookmark this Post
The best way to go here is to put the options.
And only select options that is any option more than 1 will not satisfy.
Only options less than 1 will satisfy since the power is negative.

Posted from my mobile device
User avatar
Chethan92
User avatar
Joined: 18 Jul 2018
Last visit: 21 Apr 2022
Posts: 901
Own Kudos:
1,509
Given Kudos: 95
Location: India
Concentration: Operations, General Management
Schools: IIMB EPGP'22 (M)
GMAT 1: 590 Q46 V25
GMAT 2: 690 Q49 V34
WE:Engineering (Energy)
Products:
My Reviews
Schools: IIMB EPGP'22 (M)
GMAT 2: 690 Q49 V34
Posts: 901
Kudos: 1,509
If y^(-2) + 2y^(-1) - 15 = 0, which of the following could be the valu 22 Aug 2018, 17:55
Kudos
Add Kudos
Bookmarks
Bookmark this Post
funsogu
Afc0892

Sure it is a typo (since you got the answer) but -1/3 is not a root, otherwise option D will be correct too. The roots are 1/3 and -1/5 (option C). I am also an arsenal fan. Up gunners!!!


Afc0892
\(y^{-2}\) can be written as \(\frac{1}{y^2}\)
Similarly \(y^{-1}\) can be written as \(\frac{1}{y}\)

Then the equation becomes \(\frac{1}{y^2}\) + 2\(\frac{1}{y}\) - 15 = 0.

Taking LCM, the equation becomes 1+2y-15\(y^2\) = 0.

Re-arranging gives 15\(y^2\)-2y-1 = 0.

15\(y^2\)-5y+3y-1 = 0.

5y(3y-1)+1(3y-1) = 0

Either y = \(\frac{-1}{3}\) or y = \(\frac{-1}{5}\).

Among the answer choices.

y = \(\frac{-1}{5}\)

C is the answer.
Show more

Yes its typo. Thanks for mentioning. COYG ?

Posted from my mobile device
User avatar
ScottTargetTestPrep
User avatar
Target Test Prep Representative
Joined: 14 Oct 2015
Last visit: 26 Apr 2026
Posts: 22,286
Own Kudos:
26,537
Given Kudos: 302
Status:Founder & CEO
Affiliations: Target Test Prep
Location: United States (CA)
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 22,286
Kudos: 26,537
If y^(-2) + 2y^(-1) - 15 = 0, which of the following could be the valu 26 Aug 2018, 18:21
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel
If \(y^{-2} + 2y^{-1} -15 = 0\), which of the following could be the value of y?


A. \(3\)

B. \(\frac{1}{5}\)

C. \(\frac{-1}{5}\)

D. \(\frac{-1}{3}\)

E. \(-5\)
Show more

Simplifying we have:

1/y^2 + 2/y - 15 = 0

Multiplying by y^2 we have:

1 + 2y - 15y^2 = 0

15y^2 - 2y - 1 = 0

(3y - 1)(5y + 1) = 0

3y - 1 = 0 → 3y = 1 → y = 1/3

Or

5y + 1 = 0 → 5y = -1 → y = -⅕

Answer: C
User avatar
bumpbot
User avatar
Non-Human User
Joined: 09 Sep 2013
Last visit: 04 Jan 2021
Posts: 38,985
Own Kudos:
1,118
Posts: 38,985
Kudos: 1,118
If y^(-2) + 2y^(-1) - 15 = 0, which of the following could be the valu 15 Dec 2022, 09:28
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Automated notice from GMAT Club BumpBot:

A member just gave Kudos to this thread, showing it’s still useful. I’ve bumped it to the top so more people can benefit. Feel free to add your own questions or solutions.

This post was generated automatically.
Moderators:
Bunuel
Math Expert
109832 posts
Krunaal
Tuck School Moderator
852 posts