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Is x > y? (1) x^3 > 100y^7 (2) x > 0

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Intern
Joined: 13 Jun 2016
Posts: 6
Is x > y? (1) x^3 > 100y^7 (2) x > 0  [#permalink]

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29 Jun 2018, 23:58
4
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Difficulty:

85% (hard)

Question Stats:

36% (01:06) correct 64% (01:04) wrong based on 33 sessions

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Is x > y?

(1) x^3 > 100y^7
(2) x > 0
Manager
Joined: 19 Nov 2017
Posts: 93
Location: India
Schools: ISB
GMAT 1: 670 Q49 V32
GPA: 4
Re: Is x > y? (1) x^3 > 100y^7 (2) x > 0  [#permalink]

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30 Jun 2018, 00:55
Is X>Y?

A) x^3>100y^7
for any positive value of x and y if A is true, then X>Y. However, for any negative value of x and y, A is false.
INSUFFICIENT

B) X>0
CLEARLY INSUFFICIENT

A&B) x^3>100y^7 and x>0
when y is negative: A and B satisfy, and X>Y
when y is positive: A and B satisfy, but X<Y in some cases (X=1/11, Y=1/10)
INSUFFICIENT

Therefore, E.
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Math Expert
Joined: 02 Aug 2009
Posts: 6258
Is x > y? (1) x^3 > 100y^7 (2) x > 0  [#permalink]

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30 Jun 2018, 01:49
1
DarkBullRider wrote:
Is x > y?

(1) x^3 > 100y^7
(2) x > 0

few info
1) if the variable x positive
# $$x >1.... x^n$$ will be >x, where n>1.
# $$x<1.......x^n$$ will be <x, where n>1.

2) if the variable x is negative
#x to the power of EVEN integer is always >x
# $$x>-1 .... x^n$$ will be >x, where n>1 and odd,
# $$x<-1.......x^n$$will be <x, where n>1 and odd,

(1) $$x^3 > 100y^7$$
if x and y are positive integers x>y... $$5^3>100*1^7$$
but if both are positive fractions, x can be <y....$$\frac{1}{100}^3>100*\frac{2}{100}^7.....\frac{1}{10^6}>100*\frac{128}{10^14}=\frac{0.128}{10^9}$$
If negative , similarly we can find
but different answers even when both are positive
insuff

(2) x > 0
insuff

combined..
two cases as mentioned in case 1 exist
if x and y are positive integers x>y... $$5^3>100*1^7$$
but if both are positive fractions, x can be <y....$$\frac{1}{100}^3>100*\frac{2}{100}^7.....\frac{1}{10^6}>100*\frac{128}{10^14}=\frac{0.128}{10^9}$$
E
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1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html

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Is x > y? (1) x^3 > 100y^7 (2) x > 0 &nbs [#permalink] 30 Jun 2018, 01:49
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