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

 It is currently 27 Aug 2014, 11:33

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

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

Root rule question

Author Message
TAGS:
Intern
Joined: 24 Jul 2009
Posts: 29
Followers: 0

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

Root rule question [#permalink]  16 Aug 2011, 14:36
00:00

Difficulty:

5% (low)

Question Stats:

57% (02:32) correct 43% (01:21) wrong based on 7 sessions
So here is the question:

The function f is defined by subtracting 25 from the square of a number and the function g is defined as the square root of one-half of a number. If g(f(x))=10, then which of the following is a possible value of x?

a) -15
b)-5
c) 0
d) 5
e) 25

My question is when setting up part of the equation, should I take [/square_root](x/2) or the [/square_root]of x and then divide two...does the root encompass both the numerator and denominator. In my mind, it encompasses both and when I take root two to the other side, I don't get the official answer. What am I not understanding correctly? I'm just brushing up on math rules and would appreciate any help!
[Reveal] Spoiler: OA
Director
Joined: 01 Feb 2011
Posts: 770
Followers: 14

Kudos [?]: 81 [1] , given: 42

Re: Root rule question [#permalink]  16 Aug 2011, 17:46
1
KUDOS
f(x) = x^2-25
g(x) = sqrt(x/2) not sqrt(x)/2, because the question clearly says its square root of (half of the number).

g(f(x)) = 10

g(x^2-25) =10

sqrt((x^2-25)/2) = 10

=> (x^2-25)/2 = 100
=>x^2 = 225

=> x = 15 or -15

Manager
Joined: 18 Mar 2010
Posts: 90
Location: United States
GMAT 1: Q V
Followers: 2

Kudos [?]: 26 [0], given: 5

Re: Root rule question [#permalink]  16 Aug 2011, 18:49
the square root of one-half of a number.

Agree with Spidy. Would have been the other way if it had read "one half the square root of a number."
Intern
Joined: 24 Jul 2009
Posts: 29
Followers: 0

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

Re: Root rule question [#permalink]  16 Aug 2011, 20:18
@mmphf and @spidy001 thanks guys! Yeah, after I went through it one more time I got the right answer...a simple mistake carrying out the equation cost me the answer the first time around.
Re: Root rule question   [#permalink] 16 Aug 2011, 20:18
Similar topics Replies Last post
Similar
Topics:
General Math Rule Question 2 10 Jan 2012, 17:01
6 Power rules question 4 15 Oct 2011, 11:26
Question on roots 3 30 Apr 2011, 19:20
Square Root Rules 0 25 Jul 2009, 05:21
root question 5 27 Dec 2006, 06:43
Display posts from previous: Sort by