It is currently 12 Aug 2020, 09:32

### 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

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

# If the operation @ is defined by x@y=(xy)^1/2 for all

Author Message
TAGS:
Founder
Joined: 18 Apr 2015
Posts: 12607
Followers: 268

Kudos [?]: 3169 [0], given: 11654

If the operation @ is defined by x@y=(xy)^1/2 for all [#permalink]  27 Jul 2020, 09:00
Expert's post
00:00

Question Stats:

84% (00:27) correct 15% (01:18) wrong based on 13 sessions
If the operation @ is defined by $$x@y=\sqrt{xy}$$ for all positive numbers x and y, then (5@45)@60 =

(A) 30
(B) 60
(C) 90
(D) $$30\sqrt{15}$$
(E) $$60\sqrt{15}$$
[Reveal] Spoiler: OA

_________________

Need Practice? 20 Free GRE Quant Tests available for free with 20 Kudos
GRE Prep Club Members of the Month: Each member of the month will get three months free access of GRE Prep Club tests.

Founder
Joined: 18 Apr 2015
Posts: 12607
Followers: 268

Kudos [?]: 3169 [0], given: 11654

Re: If the operation @ is defined by x@y=(xy)^1/2 for all [#permalink]  27 Jul 2020, 09:02
Expert's post
Post A Detailed Correct Solution For The Above Questions And Get A Kudos.
Question From Our New Project: GRE Quant Challenge Questions Daily - NEW EDITION!

_________________

Need Practice? 20 Free GRE Quant Tests available for free with 20 Kudos
GRE Prep Club Members of the Month: Each member of the month will get three months free access of GRE Prep Club tests.

Intern
Joined: 10 Aug 2019
Posts: 19
Followers: 0

Kudos [?]: 6 [1] , given: 2

Re: If the operation @ is defined by x@y=(xy)^1/2 for all [#permalink]  27 Jul 2020, 09:51
1
KUDOS
x@y = \sqrt{xy}
5@45 = \sqrt{5*45} = \sqrt{5*5*9} = 5*3 = 15
15@60 = \sqrt{15*50} = \sqrt{15*15*4} = 15*2 = 30

Ans : A) 30
GRE Instructor
Joined: 10 Apr 2015
Posts: 3672
Followers: 142

Kudos [?]: 4236 [0], given: 67

Re: If the operation @ is defined by x@y=(xy)^1/2 for all [#permalink]  27 Jul 2020, 12:29
Expert's post
Carcass wrote:
If the operation @ is defined by $$x@y=\sqrt{xy}$$ for all positive numbers x and y, then (5@45)@60 =

(A) 30
(B) 60
(C) 90
(D) $$30\sqrt{15}$$
(E) $$60\sqrt{15}$$

We want to evaluate: (5 @ 45) @ 60

(5 @ 45) = √[(5)(45)]
= √225
= 15

So, (5 @ 45) @ 60 = 15 @ 60
From here, 15 @ 60 = √[(15)(60)]
= √900
= 30

_________________

Brent Hanneson – Creator of greenlighttestprep.com
If you enjoy my solutions, you'll like my GRE prep course.

Intern
Joined: 25 Jul 2020
Posts: 30
Followers: 0

Kudos [?]: 14 [0], given: 2

Re: If the operation @ is defined by x@y=(xy)^1/2 for all [#permalink]  28 Jul 2020, 01:15
(5@45)@60

$$\sqrt{\sqrt{5 \times 45} \times 60}$$
$$\sqrt{\sqrt{225} \times 60}$$
$$\sqrt{900}$$
= 30
Re: If the operation @ is defined by x@y=(xy)^1/2 for all   [#permalink] 28 Jul 2020, 01:15
Display posts from previous: Sort by