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could be x³?

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by sanju09 » Sat Jul 24, 2010 3:05 am
If x is an integer, which of the following could be x³?
I. 1.25 x 10^17
II. 12.5 x 10^-12
III. 0.125 x 10^-12
A. I only
B. II only
C. I and II only
D. I and III only
E. II and III only

[spoiler]Source: majortests.com[/spoiler]
The mind is everything. What you think you become. -Lord Buddha



Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001

www.manyagroup.com
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Source: — Problem Solving |

by outreach » Sat Jul 24, 2010 3:07 am
A
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by selango » Sat Jul 24, 2010 3:08 am
Option A: 1.25*10^17

125*10^15=x^3-->x=5*10^5

Option B and C rule out as they are not integer.[Since x is an integer,x^3 also is an integer]

Pick A
Last edited by selango on Sat Jul 24, 2010 3:17 am, edited 1 time in total.
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by sanju09 » Sat Jul 24, 2010 3:15 am
@outreach and selango

Please let us also know how you pick an answer choice, may be in very epigrammatic mode. This would bring about a discussion if contradictions were there in concepts rather than in an answer choice and that would be helpful to the less active users of this site at large.
The mind is everything. What you think you become. -Lord Buddha



Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001

www.manyagroup.com
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by aloneontheedge » Sat Jul 24, 2010 10:27 am
selango wrote:Option A: 1.25*10^17

125*10^15=x^3-->x=5*10^5

Option B and C rule out as they are not integer.[Since x is an integer,x^3 also is an integer]

Pick A
0.125*10^-12 = 125*10^-15
X = (5 * 10^-5)^3 = 125 *10^-15
Pick D
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by gmatmachoman » Sat Jul 24, 2010 10:54 am
sanju09 wrote:If x is an integer, which of the following could be x³?
I. 1.25 x 10^17
II. 12.5 x 10^-12
III. 0.125 x 10^-12
A. I only
B. II only
C. I and II only
D. I and III only
E. II and III only

[spoiler]Source: majortests.com[/spoiler]
1.X ^3 = 1.25 x 10^17 = 125 X 10^15

X = 5 X 10 ^3 -- Integer

II .X ^3 =12.5 x 10^-12 = 12.5/ 10^12
=125/10^13

X= 5 / 10 ^(13/3) --- NOT a integer.

III. X ^3 =0.125 x 10^-12 = 0.125/10^12
125/10^15
X= 5/10^5 -- NOT a integer.

Pick A
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