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# Ix x>3?

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Intern
Joined: 17 Nov 2013
Posts: 39

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Updated on: 16 Oct 2015, 05:07
2
1
00:00

Difficulty:

65% (hard)

Question Stats:

55% (01:40) correct 45% (01:54) wrong based on 126 sessions

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Is x>3?

1) $$5^y > 25^8$$ and $$y=x^2$$
2) $$2^{15x} > 8^{4x}*8$$

Originally posted by harish1986 on 14 Oct 2015, 12:06.
Last edited by ENGRTOMBA2018 on 16 Oct 2015, 05:07, edited 2 times in total.
Formatted the question, updated the OA and renamed the topic
Intern
Joined: 02 Oct 2015
Posts: 11
Location: Uzbekistan
Concentration: Entrepreneurship, Strategy
GMAT 1: 570 Q39 V29
GPA: 3.9
WE: General Management (Pharmaceuticals and Biotech)

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14 Oct 2015, 12:33
2) 2^15x > (8^4x)(8)
Am I right that we have finally here
2^15x>2^15x ? (imagining 8 as 2^3)
Intern
Joined: 17 Nov 2013
Posts: 39

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14 Oct 2015, 22:15
Amidro wrote:
2) 2^15x > (8^4x)(8)
Am I right that we have finally here
2^15x>2^15x ? (imagining 8 as 2^3)

Here is the clarification

==>(8^4x)*(8) can be written as (2^(3*4x)) * (2^3)=2^(12x+3).
==>(2^a) *(2^b)= 2^(a+b)
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 8805
Location: Pune, India

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14 Oct 2015, 23:14
3
harish1986 wrote:
Is x>3?

1) $$5^y > 25^8$$ and $$y=x^2$$
2) $$2^{15x} > 8^{4x}*8$$

1) $$5^y > 25^8$$ and $$y=x^2$$
$$5^y > (5^2)^8$$
$$5^y > 5^{16}$$
So $$y > 16$$
$$x^2 > 16$$
$$|x| > 4$$
$$x < -4$$ or $$x > 4$$
Not sufficient.

2) $$2^{15x} > 8^{4x}*8$$
$$2^{15x} > 2^{12x}*2^3$$
$$2^{15x} > 2^{12x+3}$$
15x > 12x + 3
x > 1
Not sufficient.

Both together, we know that x must be greater than 4.

_________________

Karishma
Veritas Prep GMAT Instructor

Intern
Joined: 02 Oct 2015
Posts: 11
Location: Uzbekistan
Concentration: Entrepreneurship, Strategy
GMAT 1: 570 Q39 V29
GPA: 3.9
WE: General Management (Pharmaceuticals and Biotech)

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15 Oct 2015, 03:27
VeritasPrepKarishma wrote:
harish1986 wrote:
Is x>3?

1) $$5^y > 25^8$$ and $$y=x^2$$
2) $$2^{15x} > 8^{4x}*8$$

1) $$5^y > 25^8$$ and $$y=x^2$$
$$5^y > (5^2)^8$$
$$5^y > 5^{16}$$
So $$y > 16$$
$$x^2 > 16$$
$$|x| > 4$$
$$x < -4$$ or $$x > 4$$
Not sufficient.

2) $$2^{15x} > 8^{4x}*8$$
$$2^{15x} > 2^{12x}*2^3$$
$$2^{15x} > 2^{12x+3}$$
15x > 12x + 3
x > 1
Not sufficient.

Both together, we know that x must be greater than 4.

If 5^y is > than 5^16
Meaning y=17 and thus making it positive (if negative, statement 1 is not true)
Could you please clarify (y cannot equal 16, it is MORE than 16, meaning at least "17"?)
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 8805
Location: Pune, India

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15 Oct 2015, 21:03
1
Amidro wrote:
VeritasPrepKarishma wrote:
harish1986 wrote:
Is x>3?

1) $$5^y > 25^8$$ and $$y=x^2$$
2) $$2^{15x} > 8^{4x}*8$$

1) $$5^y > 25^8$$ and $$y=x^2$$
$$5^y > (5^2)^8$$
$$5^y > 5^{16}$$
So $$y > 16$$
$$x^2 > 16$$
$$|x| > 4$$
$$x < -4$$ or $$x > 4$$
Not sufficient.

2) $$2^{15x} > 8^{4x}*8$$
$$2^{15x} > 2^{12x}*2^3$$
$$2^{15x} > 2^{12x+3}$$
15x > 12x + 3
x > 1
Not sufficient.

Both together, we know that x must be greater than 4.

If 5^y is > than 5^16
Meaning y=17 and thus making it positive (if negative, statement 1 is not true)
Could you please clarify (y cannot equal 16, it is MORE than 16, meaning at least "17"?)

x and y needn't be integers. So y > 16 means y could be 16.2 or 16.348 or 17 or 18 or 267 etc.

y cannot be negative but x can be. y is greater than 16 means that absolute value of x is greater than 4 (because y = x^2)
If x is 5, x^2 = 25 = y (positive y greater than 16)
If x is -5, x^2 = 25 = y (positive y greater than 16)
_________________

Karishma
Veritas Prep GMAT Instructor

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29 Mar 2017, 04:41
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Re: Ix x>3? &nbs [#permalink] 29 Mar 2017, 04:41
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