Equations

This topic has expert replies
Legendary Member
Posts: 708
Joined: Sun Jun 01, 2008 4:59 am
Location: USA
Thanked: 13 times
Followed by:1 members

Equations

by niraj_a » Wed Aug 26, 2009 6:23 pm
If x^2/9 - 4/y^2 = 12, what is the value of x?

(1) x/3 + 2/y = 6

(2) x/3 - 2/y = 2

Those blobs stand for negative

Master | Next Rank: 500 Posts
Posts: 121
Joined: Thu Jun 11, 2009 1:16 am
Thanked: 4 times
GMAT Score:720

by Naruto » Wed Aug 26, 2009 10:12 pm
IMO D

Each alone is sufficient,
the equation is of form a^2-b^2, i.e (a+b) x (a-b)

if a+b is given we can find value of a-b and then solving the two the value of a

Same goes for a-b.

Legendary Member
Posts: 708
Joined: Sun Jun 01, 2008 4:59 am
Location: USA
Thanked: 13 times
Followed by:1 members

by niraj_a » Wed Aug 26, 2009 10:38 pm
i see naruto. here's my question though -

say in 1) we arbitrarily square the whole string, so we get

x^2/9 + 4/y^2 = 36

so we add the stem and this result to get

2(x^2/9) = 36
(x^2) = 2
so x = + or - 1.41

the same issue happens if you square statement 2. where did i go wrong? it doesnt say anywhere is x or y are integers or -ve.

Newbie | Next Rank: 10 Posts
Posts: 6
Joined: Sat Jul 18, 2009 2:51 am
Location: UK
GMAT Score:650

by KK9_GMAT » Thu Aug 27, 2009 1:39 am
niraj_a,

When you square 1) ie. (x/3 + 2/y)^2 = 6^2,
using (a+b)^2 = a^2 + 2ab + b^2

we get, (x^2/9) + 2((x/3)*(2/y)) + (4/y^2) = 36
(x^2/9) + (4x/3y) + (4/y^2) = 36

which is not equal to what you calculated.
I think this is where you might have gone wrong.

Legendary Member
Posts: 708
Joined: Sun Jun 01, 2008 4:59 am
Location: USA
Thanked: 13 times
Followed by:1 members

by niraj_a » Thu Aug 27, 2009 4:27 am
kudos, thanks much.

i guess i'll never score high on the quant....

Newbie | Next Rank: 10 Posts
Posts: 6
Joined: Sat Jul 18, 2009 2:51 am
Location: UK
GMAT Score:650

by KK9_GMAT » Thu Aug 27, 2009 6:19 am
No worries. Better to commit mistakes now than in the actual exam. :)

Master | Next Rank: 500 Posts
Posts: 208
Joined: Sat Jan 31, 2009 11:32 am
Location: Mumbai
Thanked: 2 times

Re: Equations

by vikram_k51 » Thu Aug 27, 2009 11:48 pm
niraj_a wrote:If x^2/9 - 4/y^2 = 12, what is the value of x?

(1) x/3 + 2/y = 6

(2) x/3 - 2/y = 2

Those blobs stand for negative
Answer will be D.

Master | Next Rank: 500 Posts
Posts: 128
Joined: Thu Jul 30, 2009 1:46 pm
Thanked: 1 times

Re: Equations

by fruti_yum » Tue Sep 01, 2009 10:10 am
vikram_k51 wrote:
niraj_a wrote:If x^2/9 - 4/y^2 = 12, what is the value of x?

(1) x/3 + 2/y = 6

(2) x/3 - 2/y = 2

Those blobs stand for negative
Answer will be D.
When i solve each of the statements , i get either y = 6 or x = 12 for both individually..

Where do i go from there in the question stem?