Last visit was: 27 Apr 2026, 20:15 It is currently 27 Apr 2026, 20:15
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
   1   2 
User avatar
exc4libur
User avatar
Joined: 24 Nov 2016
Last visit: 22 Mar 2022
Posts: 1,680
Own Kudos:
1,469
Given Kudos: 607
Location: United States
Posts: 1,680
Kudos: 1,469
If the operation ? is defined by x?y = yx^(1/2) for all positive 19 Aug 2019, 12:53
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Quote:
If the operation ? is defined by x?y=y√x for all positive integers x and y, then 9?(16?25)=

A. 60
B. 180
C. 240
D. 300
E. 1200
Show more

16?25=25√16=25•4=100
9?100=100√9=300

Answer (D).
User avatar
Mohammadmo
User avatar
Joined: 29 Jun 2019
Last visit: 03 Nov 2022
Posts: 346
Own Kudos:
250
Given Kudos: 16
Posts: 346
Kudos: 250
If the operation ? is defined by x?y = yx^(1/2) for all positive 19 Aug 2019, 14:07
Kudos
Add Kudos
Bookmarks
Bookmark this Post
First we should indicate the term in the parenthesis.
X=16,Y=25
25×4=100
9?100 ==>100×3=300
Option D

Posted from my mobile device
User avatar
vaibhav1221
User avatar
Joined: 19 Nov 2017
Last visit: 24 Jul 2025
Posts: 292
Own Kudos:
410
Given Kudos: 50
Location: India
Schools: IIMA '25 (A) Columbia CBS'26 (D) Fuqua '26 (D) ISB '25 (WL) Darden '26 (D) Kenan-Flagler '26 (WL)
GMAT 1: 710 Q49 V38
GPA: 3.25
WE:Account Management (Advertising and PR)
Schools: IIMA '25 (A) Columbia CBS'26 (D) Fuqua '26 (D) ISB '25 (WL) Darden '26 (D) Kenan-Flagler '26 (WL)
GMAT 1: 710 Q49 V38
Posts: 292
Kudos: 410
If the operation ? is defined by x?y = yx^(1/2) for all positive 19 Aug 2019, 21:44
Kudos
Add Kudos
Bookmarks
Bookmark this Post
\(x?y = y\sqrt{x}\)

\(? = \sqrt{x}/x\)

9?(16?25) =

Solve the bracket first.

\((\sqrt{16}*25)\) \(= 4*25 = 100\)

\(\sqrt{9}*100 = 3*100 = 300\)

Answer: 300
User avatar
lacktutor
User avatar
Joined: 25 Jul 2018
Last visit: 23 Oct 2023
Posts: 658
Own Kudos:
1,447
Given Kudos: 69
Posts: 658
Kudos: 1,447
If the operation ? is defined by x?y = yx^(1/2) for all positive 19 Aug 2019, 22:02
Kudos
Add Kudos
Bookmarks
Bookmark this Post
If the operation ? is defined by x?y=y√x for all positive integers x and y, then 9?(16?25)=

x?y=y√x
x?y=\(yx^{\frac{1}{2}}\)
?=1/2 - the square root of a positive number

--> 9?(16?25)=\(9^{\frac{1}{2}}(16^{\frac{1}{2}}*25)\)=3*4*25=300

The answer is D.
User avatar
Hazel1134
User avatar
Joined: 02 May 2019
Last visit: 21 Oct 2019
Posts: 7
Own Kudos:
10
Given Kudos: 6
Posts: 7
Kudos: 10
If the operation ? is defined by x?y = yx^(1/2) for all positive 19 Aug 2019, 22:28
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Lets not forget about PEMDAS for this question! :O
Although i am pretty sure most of us here will not!

Now, the ones in the Para first -- 16?25 = 25*sqrt16 = 25 * 4 = 100.

Next, it becomes 9?100. Again, 100 * sqrt9 = 100 * 3 = 300.

Hence, D is and should be the answer.
   1   2 
Moderators:
Bunuel
Math Expert
109929 posts
Krunaal
Tuck School Moderator
852 posts