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could be x³?

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could be x³?

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]
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by outreach » Sat Jul 24, 2010 3:07 am
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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.
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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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