Last visit was: 12 May 2025, 02:32 It is currently 12 May 2025, 02:32
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.
Close
Request Expert Reply
Confirm Cancel
User avatar
vwjetty
User avatar
Retired Moderator
Joined: 25 Apr 2010
Last visit: 02 Apr 2014
Posts: 897
Own Kudos:
571
 [96]
Given Kudos: 71
Status:battlecruiser, operational...
Schools: Carey '16
Schools: Carey '16
Posts: 897
Kudos: 571
 [96]
8
Kudos
Add Kudos
88
Bookmarks
Bookmark this Post
Most Helpful Reply
User avatar
KarishmaB
Joined: 16 Oct 2010
Last visit: 11 May 2025
Posts: 15,959
Own Kudos:
73,054
 [41]
Given Kudos: 467
Location: Pune, India
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 15,959
Kudos: 73,054
 [41]
23
Kudos
Add Kudos
18
Bookmarks
Bookmark this Post
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 12 May 2025
Posts: 101,323
Own Kudos:
Given Kudos: 93,456
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 101,323
Kudos: 723,549
 [25]
8
Kudos
Add Kudos
15
Bookmarks
Bookmark this Post
General Discussion
User avatar
kraizada84
Joined: 13 Mar 2012
Last visit: 19 Nov 2018
Posts: 152
Own Kudos:
503
 [1]
Given Kudos: 48
Concentration: Operations, Strategy
Posts: 152
Kudos: 503
 [1]
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Smita04
Which of the following best approximates the value of q if 5^28 + 3^11 = 5^q ?
(A) 39
(B) 30
(C) 28
(D) 27
(E) 17

Pay attention to the funda here that 3^11 is much less than 5^28 (obviously its superlarge number)

hence q can be approximated to 28.

ANALOGY: suppose you need to add 10...... trillion to 100 then obviously the result after addition can be approximated to 10......trillion.

Hence C
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 12 May 2025
Posts: 101,323
Own Kudos:
723,549
 [3]
Given Kudos: 93,456
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 101,323
Kudos: 723,549
 [3]
Kudos
Add Kudos
3
Bookmarks
Bookmark this Post
User avatar
gmat6nplus1
Joined: 04 Oct 2013
Last visit: 09 Jan 2019
Posts: 141
Own Kudos:
653
 [4]
Given Kudos: 29
Concentration: Finance, Leadership
GMAT 1: 590 Q40 V30
GMAT 2: 730 Q49 V40
WE:Project Management (Media/Entertainment)
GMAT 2: 730 Q49 V40
Posts: 141
Kudos: 653
 [4]
4
Kudos
Add Kudos
Bookmarks
Bookmark this Post
I solved it this way:

\(5^2^8+3^1^1=5^q\)

\(3^3=27\) which is pretty close to \(5^2\)
\(3^1^1\) is 3 times \(3^3\) and one time \(3^2\) thus we can approximate to 3 times \(5^2\) and one 5

\(5^2^8+5^7=5^7(5^2^1+1)\).

we can conclude that the best approximation is \(5^2^8\) since \(5^2^1+1\) is a little bit more than \(5^2^1\). and \(5^7\) times (a little bit more than \(5^2^1\)) = around \(5^2^8\)

hope it helps.
User avatar
arunspanda
Joined: 04 Oct 2013
Last visit: 31 Oct 2021
Posts: 127
Own Kudos:
319
 [4]
Given Kudos: 55
Location: India
GMAT Date: 05-23-2015
GPA: 3.45
Products:
Posts: 127
Kudos: 319
 [4]
4
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Which of the following best approximates the value of q if \(5^{28} + 3^{11} = 5^q\) ?
(A) 39
(B) 30
(C) 28
(D) 27
(E) 17


\(5^{28} + 3^{11} = 5^q\)

Or, \(5^{28}( 1 + \frac{3^{11}}{5^{28}}) = 5^q\)

Since, \(\frac{3^{11}}{5^{28}} << 1\), the term \((1 + \frac{3^{11}}{5^{28}})\)can be approximated to 1.

Thus, \(5 ^ {28} = 5 ^q\)

Or, \(q = 28\).

Answer: (C)
User avatar
GMATGuruNY
Joined: 04 Aug 2010
Last visit: 09 May 2025
Posts: 1,346
Own Kudos:
3,588
 [2]
Given Kudos: 9
Schools:Dartmouth College
Expert
Expert reply
Posts: 1,346
Kudos: 3,588
 [2]
2
Kudos
Add Kudos
Bookmarks
Bookmark this Post
vwjetty
Which of the following best approximates the value of q if \(5^{28}+3^{11}=5^q\) ?

A. 39
B. 30
C. 28
D. 27
E. 17

\(5^q - 5^{28} = 3^{11}\)

We can PLUG IN THE ANSWERS, which represent the approximate value of q.

B: q=30
\(5^{30} - 5^{28} = 3^{11}\)
\(5^{28}(5^2 - 1) = 3^{11}\)
\(5^{28}(24) = 3^{11}\)
Not viable.
The left side is MUCH GREATER than the right side.
Eliminate B.

D: q=27
\(5^{27} - 5^{28} = 3^{11}\)
Not viable.
The left side is negative and thus is MUCH SMALLER than the right side.
Eliminate D.

Since B makes the left side too big, while D makes the left side too small, the correct answer must be BETWEEN B AND D.

avatar
Solas
Joined: 24 Sep 2017
Last visit: 28 Nov 2024
Posts: 1
Given Kudos: 7
Posts: 1
Kudos: 0
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Please could you help me tell if the below solution is an acceptable approach?

5^28 will yield a value with units digit 0
3^11 will yield a vaule with units digit 1

The sum of these two values will yield a number with units digit 1. Since 5^q would yield a value only with units digit 0 or 5, the closest approximation to '1' above would be '0' - and only an even power for 5 would give us a unit digit '0'. Therefore, q=EVEN -> hence C

Appreciate your help in advance
User avatar
bumpbot
User avatar
Non-Human User
Joined: 09 Sep 2013
Last visit: 04 Jan 2021
Posts: 36,874
Own Kudos:
Posts: 36,874
Kudos: 979
Kudos
Add Kudos
Bookmarks
Bookmark this Post
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.
Moderators:
Math Expert
101323 posts
PS Forum Moderator
580 posts