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by diebeatsthegmat » Sat May 14, 2011 6:42 am
15. If sˆ4v³xˆ7 < 0 (a), is svx < 0?
(1) v < 0
(2) x > 0

[spoiler]we surely know that s^4>0 so v^3*x^7<0 it means v<0 or x<0
1. if v<0 from a we can know x>0 so sufficient
if x>0 and from a we can know v<0, sufficient, the answer is D.
why is it E?[/spoiler]
16:
Is |v - x| < 8?
(1) v and x are integers.
(2) |v| = 4 and |x| = 6

i dont understand why the answer is EE. my answer is D and E for 15, 16
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by MAAJ » Sat May 14, 2011 7:30 am
15. If (s^4)(v³)(x^7) < 0, is svx < 0?
One of s,v,x is negative an the others positive?
Are s,v,x all positive?

(s^4)(v³)(x^7) < 0
(s^4)(v³)(x^7) < 0
(+) (?) (?) < 0
From this we know that s could be positive or negative and the result will always be positive, and that one of the other parenthesis must be negative.

(1) v < 0
If v is negative then: (+) (-) (?) < 0; thus x must be positive.
So far we know that:
s = -/+
v = -
x = +
We can't determine if svx will be positive or negative.

(2) x > 0
If x is positive then: (+) (?) (+) < 0; thus v must be negative.
So far we know that:
s = -/+
v = -
x = +
We can't determine if svx will be positive or negative.

(3) Combined:
We still can't find the sign of s, as it could be positive or negative, hence the answer must be [spoiler](E)[/spoiler]


-------------------------------------------------



16. Is |v - x| < 8?

(1) v and x are integers.
Not sufficient to answer, because we can't tell the values of V, X, or (V-X)

(2) |v| = 4 and |x| = 6
V = +/- 4
X = +/- 6

|4 - 6| = 2 < 8
|-4 - 6| = 10 > 8
Insufficient

3) Combined:
We still get the same result, as we already know that V and X are integers. Answer must be [spoiler](E)[/spoiler]

diebeatsthegmat wrote:15. If sˆ4v³xˆ7 < 0 (a), is svx < 0?
(1) v < 0
(2) x > 0

[spoiler]we surely know that s^4>0 so v^3*x^7<0 it means v<0 or x<0
1. if v<0 from a we can know x>0 so sufficient
if x>0 and from a we can know v<0, sufficient, the answer is D.
why is it E?[/spoiler]
16:
Is |v - x| < 8?
(1) v and x are integers.
(2) |v| = 4 and |x| = 6

i dont understand why the answer is EE. my answer is D and E for 15, 16
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by Geva@EconomistGMAT » Mon May 16, 2011 8:21 am
diebeatsthegmat wrote:15. If sˆ4v³xˆ7 < 0 (a), is svx < 0?
(1) v < 0
(2) x > 0

we surely know that s^4>0 so v^3*x^7<0 it means v<0 or x<0
1. if v<0 from a we can know x>0 so sufficient
if x>0 and from a we can know v<0, sufficient, the answer is D.
why is it E?


i dont understand why the answer is EE. my answer is D and E for 15, 16
15: The key here is that while s^4 is definitely positive, s itself may be positive or negative - it's the even power that makes s^4 positive. The problem is designed to trick you into equating s^4 with s. If the question had asked is s^4vx<0, your analysis would've been correct.
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