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number system

by dream700 » Wed Feb 10, 2010 4:40 am
If x and y are positive, is x^3 > y?
(1) SQ RT (x) > y
(2) x > y

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is
sufficient.
D. EACH statement ALONE is sufficient.
E. Statements (1) and (2) TOGETHER are NOT sufficient

The OA given is E. Idon't know how. help me with this. According to me the ans should be D.
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Source: — Data Sufficiency |
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by thephoenix » Wed Feb 10, 2010 5:05 am
IMO E

If x and y are positive, is x^3 > y?
(1) SQ RT (x) > y

plug values
for x=1/4 and y=1/3
s1) is true and x^3 is not > y
but for x=9 and y=2
s1) is true and x^3 > y

two diff possibilities hence insuff
(2) x > y
similarly for fractional value and for int we two ans hence insuff

s1) +s2) same

hence E
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by sanju09 » Thu Feb 11, 2010 3:31 am
dream700 wrote:If x and y are positive, is x^3 > y?
(1) SQ RT (x) > y
(2) x > y

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is
sufficient.
D. EACH statement ALONE is sufficient.
E. Statements (1) and (2) TOGETHER are NOT sufficient

The OA given is E. Idon't know how. help me with this. According to me the ans should be D.
(1) If square root of one positive number (x) is greater than another positive number(y), then the following two cases are possible:

(i) x^3 > y, when x = 9 and y = 2.

(ii) x^3 < y, when x = 0.1 and y = 0.3.

Insufficient

(2) If x > y, then x^3 could be less or more than y, since the following two cases are possible:

(i) x^3 > y, when x = 9 and y = 2.

(ii) x^3 < y, when x = 0.3 and y = 0.1.

Insufficient

Taken together, when a positive number (x) as well as its square root each is greater than another positive number(y), then we still cannot compare x and √x as y could be too small (like 0.0000000000001) that any speculation could fail. Still insufficient

[spoiler]E[/spoiler]
The mind is everything. What you think you become. -Lord Buddha



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