the value of y?

Expert replies

sanju09: GMAT Instructor; Posts: 3650; Joined: Wed Jan 21, 2009 4:27 amFollowed by: 80 members; Location: India; Thanked: 267 times; GMAT Score:760

by sanju09 » Wed Feb 15, 2012 1:57 am

If x^3 - x^2 = 2 x and y = Â¼ x^2, then what is the value of y?
I. x is a positive integer.
II. x and y are integers.

[spoiler]made up by Sanjeev K Saxena for Avenues Abroad[/spoiler]

The mind is everything. What you think you become. -Lord Buddha

Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001

www.manyagroup.com

Like this post

Source: Beat The GMAT — Data Sufficiency | Wed Feb 15, 2012 1:57 am

pemdas: Legendary Member; Posts: 1084; Joined: Fri Apr 15, 2011 2:33 pmFollowed by: 21 members; Thanked: 158 times

by pemdas » Wed Feb 15, 2012 4:10 am

sanju09 wrote:If x^3 - x^2 = 2 x and y = Â¼ x^2, then what is the value of y?
I. x is a positive integer.
II. x and y are integers.

[spoiler]made up by Sanjeev K Saxena for Avenues Abroad[/spoiler]

it's d

question stem is simplified as x^2-x-2=0 or (x-2)(x+1)=0 with roots x=(2;-1); y=(x/2)^2 , find y?
st(1) Sufficient - we get one unique value for y, as x=2
st(2) Sufficient - we get one unique value for y, as x=-1 returns non-integer

[spoiler]?[/spoiler]

Success doesn't come overnight!

Like this post

dhiren8182: Junior | Next Rank: 30 Posts; Posts: 26; Joined: Thu Dec 04, 2008 9:19 pm; Location: Bangalore; Thanked: 1 times

by dhiren8182 » Wed Feb 15, 2012 4:31 am

Your explanation is baffling for me.
values of x=2 and -1
Substituting same to get value of y (as asked in the question )
y=1/4 x^2
STATEMENT 1:x is positive .implies value of x would be 2
so y=1/4 2^2=>1
i.e y=1
SUFFICIENT
Statement 2:x and y are integers .
if x=2 y=>1
if x=-1 y=>1/4 not an integer

here its mentioned integers(not mentioned as negative or positive)
INSUFFICIENT

My ans :A

Didn't understood your explanation for statement 2 where you have mentioned x=-1 returns non integer.
Dhiren
[/quote]

Like this post

pemdas: Legendary Member; Posts: 1084; Joined: Fri Apr 15, 2011 2:33 pmFollowed by: 21 members; Thanked: 158 times

by pemdas » Wed Feb 15, 2012 5:55 am

dhiren8182 wrote: Didn't understood your explanation for statement 2 where you have mentioned x=-1 returns non integer.
Dhiren

[/quote]
when x=-1, y is non integer.
Are you sure your reasoning is correct? The question stem supplies two possibilities for x and we need additional information to determine the one (unique) value of y. The question is asking: What IS the value? . We need one value for y.

statement(2) x and y are integers. must be Sufficient

dhiren8182 wrote: Statement 2:x and y are integers .
if x=2 y=>1
if x=-1 y=>1/4 not an integer

here its mentioned integers(not mentioned as negative or positive)
INSUFFICIENT

By knowing that y is integer (regardless positive or negative) you decide about sufficiency here, as another value of y is non integer (that's what I meant)

[spoiler]this is very easy question.
since you hit the permutation of 'experts@BTG', i guess you've just over-analyzed[/spoiler]

Success doesn't come overnight!

Like this post

dhiren8182: Junior | Next Rank: 30 Posts; Posts: 26; Joined: Thu Dec 04, 2008 9:19 pm; Location: Bangalore; Thanked: 1 times

by dhiren8182 » Wed Feb 15, 2012 7:56 pm

Got it...
Silly mistake...
Dhiren

Like this post

[email protected]: Legendary Member; Posts: 934; Joined: Tue Nov 09, 2010 5:16 amFollowed by: 14 members; Location: AAMCHI MUMBAI LOCAL; Thanked: 63 times

by [email protected] » Wed Feb 15, 2012 9:15 pm

According to me the answer is E. After applying each of the statements also, I am not getting one specific value of y.

Hence E...

OA please...

IT IS TIME TO BEAT THE GMAT

LEARNING, APPLICATION AND TIMING IS THE FACT OF GMAT AND LIFE AS WELL... KEEP PLAYING!!!

Whenever you feel that my post really helped you to learn something new, please press on the 'THANK' button.

Like this post

sanju09: GMAT Instructor; Posts: 3650; Joined: Wed Jan 21, 2009 4:27 amFollowed by: 80 members; Location: India; Thanked: 267 times; GMAT Score:760

by sanju09 » Wed Feb 15, 2012 11:15 pm

pemdas wrote:
sanju09 wrote:If x^3 - x^2 = 2 x and y = Â¼ x^2, then what is the value of y?
I. x is a positive integer.
II. x and y are integers.

[spoiler]made up by Sanjeev K Saxena for Avenues Abroad[/spoiler]
it's d

question stem is simplified as x^2-x-2=0 or (x-2)(x+1)=0 with roots x=(2;-1); y=(x/2)^2 , find y?
st(1) Sufficient - we get one unique value for y, as x=2
st(2) Sufficient - we get one unique value for y, as x=-1 returns non-integer

[spoiler]?[/spoiler]

If x^3 - x^2 = 2 x then x = 0, -1, and 2, hence y = 0, Â¼, and 1.

I. If x is a positive integer then it must be 2, hence y = 1. Sufficient

II. We don't need to know again that x is an integer. What's important to note here is that y is an integer, hence y = 0, 1; two values! Insufficient

[spoiler]OA A[/spoiler]

The mind is everything. What you think you become. -Lord Buddha

Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001

www.manyagroup.com

Like this post

[email protected]: Legendary Member; Posts: 934; Joined: Tue Nov 09, 2010 5:16 amFollowed by: 14 members; Location: AAMCHI MUMBAI LOCAL; Thanked: 63 times

by [email protected] » Fri Feb 17, 2012 5:07 am

If x^3 - x^2 = 2 x and y = Â¼ x^2, then what is the value of y?
I. x is a positive integer.
II. x and y are integers.

after solving this sum very minutely, I got the answer as D because I really did not get x=0 and y=0 possibility...

Could sanju09 please explain how did it strike to you that it is also the possibility as i think we all missed out on it...

after getting the quadratic equation no one thought of going back to the original equation and putting the value as 0.

what is it that struck you for doing so... please explain and share it with us...

Like this post

ArunangsuSahu: Master | Next Rank: 500 Posts; Posts: 382; Joined: Thu Mar 31, 2011 5:47 pm; Thanked: 15 times

by ArunangsuSahu » Fri Feb 17, 2012 8:08 am

The answer is (A)

Statement 2 is not SUFFICIENT

We get two sets of values
(0,0) and (2,1)

Like this post

sanju09: GMAT Instructor; Posts: 3650; Joined: Wed Jan 21, 2009 4:27 amFollowed by: 80 members; Location: India; Thanked: 267 times; GMAT Score:760

by sanju09 » Mon Feb 20, 2012 12:48 am

[email protected] wrote:If x^3 - x^2 = 2 x and y = Â¼ x^2, then what is the value of y?
I. x is a positive integer.
II. x and y are integers.

after solving this sum very minutely, I got the answer as D because I really did not get x=0 and y=0 possibility...

Could sanju09 please explain how did it strike to you that it is also the possibility as i think we all missed out on it...

after getting the quadratic equation no one thought of going back to the original equation and putting the value as 0.

what is it that struck you for doing so... please explain and share it with us...

If x^3 - x^2 = 2 x, then

x^3 - x^2 - 2 x = 0, (we can divide both sides by x, only once we're sure that x cannot be zero, otherwise that would be an undefined state to go any further),or

x (x^2 - x - 2) = 0, or x (x - 2) (x + 1) = 0, or

x = 0, -1, 2

and the rest is same as already stated.

The mind is everything. What you think you become. -Lord Buddha

Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001

www.manyagroup.com

Like this post

pappueshwar: Master | Next Rank: 500 Posts; Posts: 234; Joined: Fri Oct 01, 2010 7:28 pmFollowed by: 4 members; Location: chennai; Thanked: 5 times

by pappueshwar » Thu Mar 15, 2012 10:19 am

sanju09 wrote:If x^3 - x^2 = 2 x and y = Â¼ x^2, then what is the value of y?
I. x is a positive integer.
II. x and y are integers.

[spoiler]made up by Sanjeev K Saxena for Avenues Abroad[/spoiler]

hi all,

i understood the fact that A is sufficient since "2"is the only solution. my doubt is the question stem uses the word " IF" then does that mean we need/ to consider or try solving the given fact with other values also?

i did that way using 3 as option then obviously stmnt 1 is incorrect

thanks

Like this post

sanju09: GMAT Instructor; Posts: 3650; Joined: Wed Jan 21, 2009 4:27 amFollowed by: 80 members; Location: India; Thanked: 267 times; GMAT Score:760

by sanju09 » Thu Mar 22, 2012 2:35 am

pappueshwar wrote:
sanju09 wrote:If x^3 - x^2 = 2 x and y = Â¼ x^2, then what is the value of y?
I. x is a positive integer.
II. x and y are integers.

[spoiler]made up by Sanjeev K Saxena for Avenues Abroad[/spoiler]
hi all,

i understood the fact that A is sufficient since "2"is the only solution. my doubt is the question stem uses the word " IF" then does that mean we need/ to consider or try solving the given fact with other values also?

i did that way using 3 as option then obviously stmnt 1 is incorrect

thanks

How is IF posing doubt here, pappueshwar?

The mind is everything. What you think you become. -Lord Buddha

Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001

www.manyagroup.com

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

560 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review