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## few princeton review DS questions from 2nd ed math workout

This topic has 4 member replies
coachy Newbie | Next Rank: 10 Posts
Joined
11 Feb 2007
Posted:
3 messages

#### few princeton review DS questions from 2nd ed math workout

Mon Feb 19, 2007 2:25 pm
On Page 222 they have thus DS question
Is it true that X < Y?
1 5x < 5y
2 zx < zy

I thought the answer should be D. They say it is A.
Explaination is that in second statement Z could be +ve or -ve.

I chose D because we are already given zx < zy. Isn't it true that we have to assume that statement 2 is true.

Similarly on page 223

the question is
If X and Y are integers, does x = y?
1) xy = y2 (2 here is square)
2) x2 = y2 (2 here is square)

I thought the answer should be again D but the book says it is C.

_________________
gogmat

kandelaki Senior | Next Rank: 100 Posts
Joined
05 Feb 2007
Posted:
37 messages
Tue Feb 20, 2007 10:46 pm
you're right.
I guess it just about z being positve or negative, nothing to do with 0.
thanks

coachy Newbie | Next Rank: 10 Posts
Joined
11 Feb 2007
Posted:
3 messages
Tue Feb 20, 2007 7:53 am
if we assume z = 0 even the 2nd statement would not be true...

zx < zy

tells us that z cannot be 0.

_________________
gogmat

jayhawk2001 Community Manager
Joined
28 Jan 2007
Posted:
789 messages
Followed by:
1 members
30
Mon Feb 19, 2007 4:02 pm
[quote="coachy"]On Page 222 they have thus DS question
Is it true that X < Y?
1 5x < 5y
2 zx < zy

I thought the answer should be D. They say it is A.
Explaination is that in second statement Z could be +ve or -ve.

I chose D because we are already given zx < zy. Isn't it true that we have to assume that statement 2 is true.

[/quote]

[size=18]x < y holds true from 5x < 5y for all values of x and y. So, (1) is
sufficient.

zx < zy does not necessarily mean x < y, as we don't know whether
z is positive or negative. So, (2) is insufficient.

Hence A.

[/size]

[quote="coachy"]
Similarly on page 223

the question is
If X and Y are integers, does x = y?
1) xy = y2 (2 here is square)
2) x2 = y2 (2 here is square)

I thought the answer should be again D but the book says it is C.[/quote]

Can you please explain why this should be D ?

(1) is sufficient as you can safely cancel out y from both sides

I'd say (2) is insufficient as x^2 = y^2 can be expressed as
(x+y)(x-y)=0 which means x = y or x=-y.

kandelaki Senior | Next Rank: 100 Posts
Joined
05 Feb 2007
Posted:
37 messages
Mon Feb 19, 2007 10:48 pm
Is it true that X < Y?
1 5x < 5y
2 zx < zy

well if we assume that z=0 then x is not < than y , they both will be 0
that is why only first choice gives sufficient explanation.......

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