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x# = x2 + 3x x§ = x2 + 2x

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GMAT Club Legend
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Joined: 07 Jun 2014
Posts: 4722
GRE 1: Q167 V156
WE: Business Development (Energy and Utilities)
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Kudos [?]: 1630 [0], given: 390

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x# = x2 + 3x x§ = x2 + 2x [#permalink] New post 24 Mar 2018, 02:27
Expert's post
00:00

Question Stats:

49% (01:12) correct 49% (01:29) wrong based on 14 sessions
x# \(= x^2 + 3x\)
x$ \(= x^2 + 2x\)

Quantity A
Quantity B
(x$)#
(x#)$


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

Drill 1
Question: 8
Page: 547
[Reveal] Spoiler: OA

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Sandy
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Re: x# = x2 + 3x x§ = x2 + 2x [#permalink] New post 25 Mar 2018, 10:54
sandy wrote:
x# \(= x^2 + 3x\)
x$ \(= x^2 + 2x\)

Quantity A
Quantity B
(x$)#
(x#)$


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

Drill 1
Question: 8
Page: 547


Why not C
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Intern
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Posts: 8
Followers: 0

Kudos [?]: 5 [1] , given: 1

Re: x# = x2 + 3x x§ = x2 + 2x [#permalink] New post 25 Mar 2018, 19:06
1
This post received
KUDOS
yell2012prime wrote:
sandy wrote:
x# \(= x^2 + 3x\)
x$ \(= x^2 + 2x\)

Quantity A
Quantity B
(x$)#
(x#)$


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

Drill 1
Question: 8
Page: 547


Why not C


x can be 0
1 KUDOS received
GMAT Club Legend
GMAT Club Legend
User avatar
Joined: 07 Jun 2014
Posts: 4722
GRE 1: Q167 V156
WE: Business Development (Energy and Utilities)
Followers: 91

Kudos [?]: 1630 [1] , given: 390

CAT Tests
Re: x# = x2 + 3x x§ = x2 + 2x [#permalink] New post 28 Mar 2018, 13:37
1
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KUDOS
Expert's post
Explanation

Whenever you have a function within another function, you have to first calculate the value of the function on the inside, and then plug that value into the function on the outside.

Plug in to test the values. If you plug in 2 for x, then, in Quantity A, 2$ = \(2^2 + 2(2) = 8\)and 8# =\(8^2 + 3(8) = 88\); in Quantity B, 2# = \(2^2 + 3(2) = 10\) and 10$ = \(10^2 + 2(10) = 120\); eliminate choices (A) and (C).

However, if you plug in 0 for x, then both quantities are 0; eliminate choice (B), and you’re left with choice (D), the correct answer.
_________________

Sandy
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Re: x# = x2 + 3x x§ = x2 + 2x [#permalink] New post 29 Mar 2018, 05:20
Well, this is a tricky question.. because (XS)# is not a function like f(g(x)) that you have to solve the inner function and use the value in the encompassing function as @ Sandy noted above. The figure (XS)# and (x#)S are both multiplication of function, not a function within a function. So the answer could be "C"... because both resolve to X^3+5X^2+6X.
Re: x# = x2 + 3x x§ = x2 + 2x   [#permalink] 29 Mar 2018, 05:20
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x# = x2 + 3x x§ = x2 + 2x

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