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.

It appears that you are browsing the GMAT Club forum unregistered!

Signing up is free, quick, and confidential.
Join other 500,000 members and get the full benefits of GMAT Club

Registration gives you:

Tests

Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.

Applicant Stats

View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more

Books/Downloads

Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

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. _________________

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

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

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

Show Tags

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. _________________

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

Show Tags

29 Mar 2015, 08:10

Expert's post

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

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

Show Tags

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.

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

Show Tags

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.

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

Show Tags

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.

Post your Blog on GMATClub We would like to invite all applicants who are applying to BSchools this year and are documenting their application experiences on their blogs to...

HBS alum talks about effective altruism and founding and ultimately closing MBAs Across America at TED: Casey Gerald speaks at TED2016 – Dream, February 15-19, 2016, Vancouver Convention Center...