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Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here. QOTD # 4 The function f is defined by  Question banks Downloads My Bookmarks Reviews Important topics
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Founder  Joined: 18 Apr 2015
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QOTD # 4 The function f is defined by [#permalink]
Expert's post 00:00

Question Stats: 72% (00:41) correct 27% (01:28) wrong based on 43 sessions
The function f is defined by $$f(\frac{x + 3}{2}) = 3x^2 - x + 5$$ for all x

 Quantity A Quantity B f(4) 75

A)The quantity in Column A is greater.
B)The quantity in Column B is greater.
C)The two quantities are equal.
D)The relationship cannot be determined from the information given.

Practice Questions
Question: 4
Page: 203
[Reveal] Spoiler: OA

_________________ Founder  Joined: 18 Apr 2015
Posts: 8412
Followers: 165

Kudos [?]: 1807  , given: 7766

Re: QOTD # 4 The function f is defined by [#permalink]
1
KUDOS
Expert's post
Explanation

Notice the first quantity that is f(4) which means our x = 4. As such, on the LHS of our equation $$\frac{x + 3}{2} = 4$$. That lead us to x = 5

Substitute this value in our function we will obtain x = 75

The best answer is C
_________________ GRE Instructor Joined: 10 Apr 2015
Posts: 2464
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Kudos [?]: 2461  , given: 34

Re: QOTD # 4 The function f is defined by [#permalink]
2
KUDOS
Expert's post
Carcass wrote:
The function f is defined by $$f(\frac{x + 3}{2}) = 3x^2 - x + 5$$ for all x

 Quantity A Quantity B f(4) 75

A)The quantity in Column A is greater.
B)The quantity in Column B is greater.
C)The two quantities are equal.
D)The relationship cannot be determined from the information given.

Practice Questions
Question: 4
Page: 203

We're told that f[(x+3)/2] = 3x² - x + 5

Quantity A tells us to INPUT a value of 4

So, we can conclude that (x+3)/2 = 4
When we solve this equation, we get x = 5
In other words, f(4) = f[(5+3)/2] = 3(5²) - 5 + 5
= 75 - 5 + 5
= 75

So...
Quantity A: f(4) = 75
Quantity B: 75

[Reveal] Spoiler:
C

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Brent Hanneson – Creator of greenlighttestprep.com Sign up for my free GRE Question of the Day emails Manager Joined: 03 Dec 2017
Posts: 65
Followers: 0

Kudos [?]: 16  , given: 20

Re: QOTD # 4 The function f is defined by [#permalink]
1
KUDOS
Carcass wrote:
Explanation

Notice the first quantity that is f(4) which means our x = 4. As such, on the LHS of our equation $$\frac{x + 3}{2} = 4$$. That lead us to x = 5

Substitute this value in our function we will obtain x = 75

The best answer is C

Thanks!
My mistake was simply plug 4 into X
actually it is f(x)=4 , so then we find out what x was. Re: QOTD # 4 The function f is defined by   [#permalink] 21 Dec 2017, 01:46
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