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

It is currently 27 Sep 2016, 14:41
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

If 5^x – 5^(x- 3) = 124*5^y, what is y in terms of x?

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

Hide Tags

2 KUDOS received
Intern
Intern
avatar
Joined: 09 Feb 2011
Posts: 11
Followers: 0

Kudos [?]: 57 [2] , given: 1

If 5^x – 5^(x- 3) = 124*5^y, what is y in terms of x? [#permalink]

Show Tags

New post 11 Feb 2011, 03:17
2
This post received
KUDOS
18
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

  15% (low)

Question Stats:

77% (02:04) correct 23% (01:08) wrong based on 400 sessions

HideShow timer Statistics

If 5^x – 5^(x- 3) = 124*5^y, what is y in terms of x?

A. x
B. x - 6
C. x - 3
D. 2x + 3
E. 2x + 6
[Reveal] Spoiler: OA

Last edited by Bunuel on 20 Sep 2012, 14:15, edited 1 time in total.
Renamed the topic and edited the question.
Expert Post
3 KUDOS received
Math Expert
User avatar
Joined: 02 Sep 2009
Posts: 34871
Followers: 6491

Kudos [?]: 82841 [3] , given: 10120

Re: ps [#permalink]

Show Tags

New post 11 Feb 2011, 05:13
3
This post received
KUDOS
Expert's post
6
This post was
BOOKMARKED
alltimeacheiver wrote:
If 5x – 5x - 3 = (124)(5y), what is y in terms of x?
A. x
B. x - 6
C. x - 3
D. 2x + 3
E. 2x + 6
Answer:


Question should read:

If 5^x – 5^(x- 3) = 124*5^y, what is y in terms of x?
A. x
B. x - 6
C. x - 3
D. 2x + 3
E. 2x + 6

\(5^x-5^{x-3}=124*5^y\) --> factor out \(5^{x-3}\): \(5^{x-3}(5^3-1)=124*5^y\) --> \(5^{x-3}=5^y\) --> bases are equal so we can equate the powers: \(y=x-3\).

Answer: C.

alltimeacheiver format the questions correctly.
_________________

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

3 KUDOS received
Senior Manager
Senior Manager
User avatar
Joined: 08 Nov 2010
Posts: 417
WE 1: Business Development
Followers: 7

Kudos [?]: 94 [3] , given: 161

GMAT ToolKit User
Re: ps [#permalink]

Show Tags

New post 18 Feb 2011, 12:17
3
This post received
KUDOS
u can also plug in x=3. makes it very simple.
_________________

GMAT Club Premium Membership - big benefits and savings

Intern
Intern
avatar
Joined: 12 Dec 2011
Posts: 12
Location: Italy
Concentration: Finance, Entrepreneurship
GMAT Date: 04-09-2013
GPA: 4
WE: Management Consulting (Consulting)
Followers: 0

Kudos [?]: 18 [0], given: 5

Re: ps [#permalink]

Show Tags

New post 20 Sep 2012, 14:05
Bunuel wrote:
alltimeacheiver wrote:
If 5x – 5x - 3 = (124)(5y), what is y in terms of x?
A. x
B. x - 6
C. x - 3
D. 2x + 3
E. 2x + 6
Answer:


Question should read:

If 5^x – 5^(x- 3) = 124*5^y, what is y in terms of x?
A. x
B. x - 6
C. x - 3
D. 2x + 3
E. 2x + 6

\(5^x-5^{x-3}=124*5^y\) --> factor out \(5^{x-3}\): \(5^{x-3}(5^3-1)=124*5^y\) --> \(5^{x-3}=5^y\) --> bases are equal so we can equate the powers: \(y=x-3\).

Answer: C.

alltimeacheiver format the questions correctly.


Hi Bunuel,
I', trying to understand your factorization, but I find some troubles when I have to factorize some value with exponent an expression like in the question (x-3 or x+4),
Could you explain me that or do you have a deck where I could dive into this argument?
Thank you in advance
Expert Post
Math Expert
User avatar
Joined: 02 Sep 2009
Posts: 34871
Followers: 6491

Kudos [?]: 82841 [0], given: 10120

Re: ps [#permalink]

Show Tags

New post 20 Sep 2012, 14:14
mario1987 wrote:
Bunuel wrote:
alltimeacheiver wrote:
If 5x – 5x - 3 = (124)(5y), what is y in terms of x?
A. x
B. x - 6
C. x - 3
D. 2x + 3
E. 2x + 6
Answer:


Question should read:

If 5^x – 5^(x- 3) = 124*5^y, what is y in terms of x?
A. x
B. x - 6
C. x - 3
D. 2x + 3
E. 2x + 6

\(5^x-5^{x-3}=124*5^y\) --> factor out \(5^{x-3}\): \(5^{x-3}(5^3-1)=124*5^y\) --> \(5^{x-3}=5^y\) --> bases are equal so we can equate the powers: \(y=x-3\).

Answer: C.

alltimeacheiver format the questions correctly.


Hi Bunuel,
I', trying to understand your factorization, but I find some troubles when I have to factorize some value with exponent an expression like in the question (x-3 or x+4),
Could you explain me that or do you have a deck where I could dive into this argument?
Thank you in advance


\(5^{x-3}(5^3-1)=124*5^y\) --> \(5^{x-3+3}-5^{x-3}=124*5^y\) --> \(5^{x}-5^{x-3}=124*5^y\).

Theory: math-number-theory-88376.html

Practice:
tough-and-tricky-exponents-and-roots-questions-125956.html
tough-and-tricky-exponents-and-roots-questions-125967.html

Hope it helps.
_________________

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

2 KUDOS received
Senior Manager
Senior Manager
User avatar
Joined: 13 Aug 2012
Posts: 464
Concentration: Marketing, Finance
GMAT 1: Q V0
GPA: 3.23
Followers: 25

Kudos [?]: 394 [2] , given: 11

GMAT ToolKit User
If 5^x – 5^(x- 3) = 124*5^y, what is y in terms of x? [#permalink]

Show Tags

New post 12 Dec 2012, 19:52
2
This post received
KUDOS
1
This post was
BOOKMARKED
\({5^{x}}\frac{124}{125}=124(5^y)\)
\(5^{x}=5^{y+3}\)
\(x=y+3-->y=x-3\)

Answer: C
_________________

Impossible is nothing to God.

Expert Post
9 KUDOS received
Veritas Prep GMAT Instructor
User avatar
Joined: 16 Oct 2010
Posts: 6914
Location: Pune, India
Followers: 1993

Kudos [?]: 12380 [9] , given: 221

If 5^x – 5^(x- 3) = 124*5^y, what is y in terms of x? [#permalink]

Show Tags

New post 13 Dec 2012, 03:25
9
This post received
KUDOS
Expert's post
4
This post was
BOOKMARKED
vaivish1723 wrote:
5^x – 5^(x- 3) = (124)(5^y), what is y in terms of x?
A. x
B. x - 6
C. x - 3
D. 2x + 3
E. 2x + 6

Oa is
[Reveal] Spoiler:
c


Finding one variable in terms of another is very simple. Assume a value for one and find the other. Then look for the option that works.

Say, x = 3 (so that x-3 becomes 0 and we are left with simple calculations)

\(5^3 - 5^{3- 3} = (124)(5^y)\)
\(1 = 5^y\)
y = 0

Now put x = 3 in the options and find out which option gives you y = 0. Only C does so answer is (C)
_________________

Karishma
Veritas Prep | GMAT Instructor
My Blog

Get started with Veritas Prep GMAT On Demand for $199

Veritas Prep Reviews

Intern
Intern
avatar
Joined: 24 Jan 2012
Posts: 10
Followers: 0

Kudos [?]: 113 [0], given: 3

Re: ps [#permalink]

Show Tags

New post 24 Sep 2013, 09:07
144144 wrote:
u can also plug in x=3. makes it very simple.


Hi,

Can you please tell why you chose only 3 to substitute x with ?
3 KUDOS received
SVP
SVP
User avatar
Status: The Best Or Nothing
Joined: 27 Dec 2012
Posts: 1858
Location: India
Concentration: General Management, Technology
WE: Information Technology (Computer Software)
Followers: 39

Kudos [?]: 1711 [3] , given: 193

If 5^x – 5^(x- 3) = 124*5^y, what is y in terms of x? [#permalink]

Show Tags

New post 26 Feb 2014, 20:47
3
This post received
KUDOS
\(5^x – 5^{(x- 3)} = 124*5^y\)

Re-write as

\(5^x – 5^{(x- 3)} = (125 - 1 ) * 5^y\)

\(5^x – 5^{(x- 3)} = 125* 5^y - 5^y\)

\(5^x – 5^{(x- 3)} = 5^{(y+3)} - 5^y\)

LHS = RHS, so equating the powers

y = x+3 ; Answer = C
_________________

Kindly press "+1 Kudos" to appreciate :)

GMAT Club Legend
GMAT Club Legend
User avatar
Joined: 09 Sep 2013
Posts: 11704
Followers: 527

Kudos [?]: 145 [0], given: 0

Premium Member
Re: If 5^x – 5^(x- 3) = 124*5^y, what is y in terms of x? [#permalink]

Show Tags

New post 28 Mar 2015, 23:00
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

Expert Post
Optimus Prep Instructor
User avatar
Joined: 06 Nov 2014
Posts: 1672
Followers: 46

Kudos [?]: 347 [0], given: 21

Re: If 5^x – 5^(x- 3) = 124*5^y, what is y in terms of x? [#permalink]

Show Tags

New post 29 Mar 2015, 08:10
alltimeacheiver wrote:
If 5^x – 5^(x- 3) = 124*5^y, what is y in terms of x?

A. x
B. x - 6
C. x - 3
D. 2x + 3
E. 2x + 6


Given that 5^x – 5^(x- 3) = 124*5^y
So, 5^(x-3+3) - 5^(x- 3) = 124*5^y
So, 5^(x-3) [5^3 - 1] = 124*5^y
So, 5^(x-3)*124 = 124*5^y
So, 5^(x-3) = 5^y
So, x-3 = y

Hence option (C).

--
Optimus Prep's GMAT On Demand course for only $299 covers all verbal and quant. concepts in detail. Visit the following link to get your 7 days free trial account: http://www.optimus-prep.com/gmat-on-demand-course
_________________

Janielle Williams

Customer Support

Special Offer: $80-100/hr. Online Private Tutoring
GMAT On Demand Course $299
Free Online Trial Hour

1 KUDOS received
Intern
Intern
avatar
Joined: 21 Feb 2015
Posts: 28
Followers: 0

Kudos [?]: 5 [1] , given: 23

If 5^x – 5^(x- 3) = 124*5^y, what is y in terms of x? [#permalink]

Show Tags

New post 07 Aug 2015, 17:29
1
This post received
KUDOS
ok this is how you solve this

you have 5^x -5^x-3 = (124) (5^y)
step 1: 5^x (1-5^-3) =(124) (5^y)
Step 2: 5^x(1 - 1/5^3) = (124) (5^y)
Step 3: 5^x(1- 1/125) = (124) (5^y)
Step 4: 5^x (125-1)/125 = (124) (5^y)
Step 5: 5^x (124/125) = (124) (5^y)
Step 6: 5^x =[(124) (5^y) (125) ]/124
Step 7: 5^x = (125) (5^y)
Step 8: 5^x = 5^3 (5^y)
Step 9: x = 3 +y --> y = x -3
for explaining purposes I broke it down in to 9 steps. It should not take you more than 5 steps to solve this in term of y.
Ryerson (Ted Rogers) Thread Master
User avatar
Joined: 27 Sep 2015
Posts: 63
Location: Canada
GMAT 1: 410 Q33 V13
WE: Management Consulting (Computer Software)
Followers: 4

Kudos [?]: 36 [0], given: 26

GMAT ToolKit User
Re: If 5^x – 5^(x- 3) = 124*5^y, what is y in terms of x? [#permalink]

Show Tags

New post 19 Dec 2015, 13:57
Rookie124 wrote:
ok this is how you solve this

you have 5^x -5^x-3 = (124) (5^y)
step 1: 5^x (1-5^-3) =(124) (5^y)
Step 2: 5^x(1 - 1/5^3) = (124) (5^y)
Step 3: 5^x(1- 1/125) = (124) (5^y)
Step 4: 5^x (125-1)/125 = (124) (5^y)
Step 5: 5^x (124/125) = (124) (5^y)
Step 6: 5^x =[(124) (5^y) (125) ]/124
Step 7: 5^x = (125) (5^y)
Step 8: 5^x = 5^3 (5^y)
Step 9: x = 3 +y --> y = x -3
for explaining purposes I broke it down in to 9 steps. It should not take you more than 5 steps to solve this in term of y.

Your answer may be right. But it is not good practice to do long steps in GMAT. Time is critical.
_________________

Discipline does not mean control. Discipline means having the sense to do exactly what is needed.

Intern
Intern
avatar
Joined: 30 Nov 2015
Posts: 9
Followers: 0

Kudos [?]: 2 [0], given: 1

Re: If 5^x – 5^(x- 3) = 124*5^y, what is y in terms of x? [#permalink]

Show Tags

New post 22 Feb 2016, 12:55
I have a very hard time believing this is a sub 600 level question
Expert Post
1 KUDOS received
Math Forum Moderator
avatar
Joined: 20 Mar 2014
Posts: 2643
GMAT 1: 750 Q49 V44
GPA: 3.7
WE: Engineering (Aerospace and Defense)
Followers: 107

Kudos [?]: 1235 [1] , given: 786

GMAT ToolKit User Premium Member Reviews Badge
If 5^x – 5^(x- 3) = 124*5^y, what is y in terms of x? [#permalink]

Show Tags

New post 22 Feb 2016, 13:06
1
This post received
KUDOS
Expert's post
secterp wrote:
I have a very hard time believing this is a sub 600 level question


The trick with GMAT quant is not the level of questions but the time constraint. For PS, you either adopt the traditional algebraic method that can sometimes very time consuming or you can use the options to your advantage as mentioned below.

Let x=3 as you have a power of 3 and I wanted non negative powers of 5. Let see if we get values of 3 or -3 or 0 or 9 or 12 (based on the 5 options given) for y when we do RHS = LHS from the given equation of 5^x – 5^(x- 3) = 124*5^y.

When x =0, the LHS becomes

5^x-5^(x-3)=5^3-5^0=125-1=124.

RHS = 124*5^y and for LHS=RHS , the only way this is possible is when y=0 , giving you y=x-3 as the correct answer. Thus, C is the correct answer.

Hope this helps.
_________________

Thursday with Ron updated list as of July 1st, 2015: http://gmatclub.com/forum/consolidated-thursday-with-ron-list-for-all-the-sections-201006.html#p1544515
Rules for Posting in Quant Forums: http://gmatclub.com/forum/rules-for-posting-please-read-this-before-posting-133935.html
Writing Mathematical Formulae in your posts: http://gmatclub.com/forum/rules-for-posting-please-read-this-before-posting-133935.html#p1096628
GMATCLUB Math Book: http://gmatclub.com/forum/gmat-math-book-in-downloadable-pdf-format-130609.html
Everything Related to Inequalities: http://gmatclub.com/forum/inequalities-made-easy-206653.html#p1582891
Inequalities tips: http://gmatclub.com/forum/inequalities-tips-and-hints-175001.html
Debrief, 650 to 750: http://gmatclub.com/forum/650-to-750-a-10-month-journey-to-the-score-203190.html

If 5^x – 5^(x- 3) = 124*5^y, what is y in terms of x?   [#permalink] 22 Feb 2016, 13:06
    Similar topics Author Replies Last post
Similar
Topics:
1 Experts publish their posts in the topic If x = y+3+4.5x and y = x+18, what is the value of x/y ? Bunuel 2 14 Jul 2016, 01:45
1 Experts publish their posts in the topic X is a prime number bigger than 10. Also, Y = X+X^3+X^5+X^7. What is Bunuel 2 07 Jun 2016, 07:35
2 Experts publish their posts in the topic Given 2x + y + z = 3 and 5x + 3y + z = 8, what is the value of x + y - Bunuel 4 09 Dec 2015, 08:41
5 Experts publish their posts in the topic If 2^y = 4^(5x + 3) and 3^(x - 7) = 9^y, what is the value of x + y ? FTS185 4 29 Nov 2014, 19:10
4 Experts publish their posts in the topic If f(x)=125/x^3, what is the value of f(5x)*f(x/5) in terms manulath 15 24 Aug 2012, 05:04
Display posts from previous: Sort by

If 5^x – 5^(x- 3) = 124*5^y, what is y in terms of x?

  new topic post reply 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®.