If x < 0 and 0 < y < 1, which of the following has

Expert replies

mitzwillrockgmat: Master | Next Rank: 500 Posts; Posts: 124; Joined: Wed May 19, 2010 10:20 pm; Thanked: 3 times; GMAT Score:1100

by mitzwillrockgmat » Thu May 20, 2010 3:44 am

If x < 0 and 0 < y < 1, which of the following has the greatest value?

A. x2
B. (xy)^2
C. (x/y )^2
D. x^2/y
E. x^2y

Yes, i know this is an easy question & the answer is c if you use values x = -1 & y=1/2 but my question is, in less than a minute how can i reach this solution? i'm timing mysle fand i ended up spending 5 minutes plugging in values before reaching this combination!

So should i just simply keep values like -1 , 1/2 etc in mind so that i can plug them in quickly or is there another approach to this?

Also other than -1, 1/2 what are other values are good for testing?

Thank you!!

Like this post

Source: Beat The GMAT — Problem Solving | Thu May 20, 2010 3:44 am

kstv: Legendary Member; Posts: 610; Joined: Fri Jan 15, 2010 12:33 amFollowed by: 2 members; Thanked: 47 times

by kstv » Thu May 20, 2010 3:53 am

y is a fraction
so 1/y will be > 1

narrow it to C and D
both are multiplied by 1/y

since 1/yÂ²> 1/y
so C

Like this post

indiantiger: Master | Next Rank: 500 Posts; Posts: 362; Joined: Fri Oct 02, 2009 4:18 amFollowed by: 1 member; Thanked: 26 times

by indiantiger » Thu May 20, 2010 4:15 pm

given x<0 {first thing check all the answer choices if you see any value that has odd power on x and rest are even powers rule that choice out as it is to maximize the value and y is +ive}

and 0<y<1

A. x^2 , keep A
B.(xy)^2, y is a fraction which will make xy smaller than x (ignoring the sign of x), keep A
C. (x/y)^2, lets say x = -5 and y = 1/4 (x/y) becomes = -20 , (x/y)^2 = 400, keep C, discard A
D. x^2/Y, lets try with the same values x^2 = 25, x^2/y = 25*4 = 100, keep C
E.x^2*y, same as B, Y is a fraction value.

I hope the explanation helps

"Single Malt is better than Blended"

Like this post

frank1: Legendary Member; Posts: 537; Joined: Fri Jan 22, 2010 10:06 pmFollowed by: 1 member; Thanked: 14 times

by frank1 » Thu May 20, 2010 6:24 pm

My approach...
read and understand question and answers (16 seconds)
x is negative and suppose y is .5 or 1/2 (5 seconds)

now when number is divided by .5 it actually increases and when multiplied it decreses...
so y in deno gives greater value (to think recall this 10 seconds)

scan answers and eliminate some and get to C and D ...15 seconds
here i was in problem
so took x=-2 and y=.5
c gave 16 where as d gave 8 only (20 seconds)

so c...

but still not under 1 minutes....this was best i could do ...that also because other 3 options were not that tricky....

Like this post

Stuart@KaplanGMAT: GMAT Instructor; Posts: 3225; Joined: Tue Jan 08, 2008 2:40 pmFollowed by: 614 members; Location: Toronto; Thanked: 1710 times; GMAT Score:800

by Stuart@KaplanGMAT » Thu May 20, 2010 6:38 pm

mitzwillrockgmat wrote:If x < 0 and 0 < y < 1, which of the following has the greatest value?

A. x2
B. (xy)^2
C. (x/y )^2
D. x^2/y
E. x^2y

Yes, i know this is an easy question & the answer is c if you use values x = -1 & y=1/2 but my question is, in less than a minute how can i reach this solution? i'm timing mysle fand i ended up spending 5 minutes plugging in values before reaching this combination!

So should i just simply keep values like -1 , 1/2 etc in mind so that i can plug them in quickly or is there another approach to this?

Also other than -1, 1/2 what are other values are good for testing?

Thank you!!

Hi,

the question is "which of the following has the greatest value" - there's no wriggle room, so no matter which numbers you pick, the same choice will be the biggest.

In other words, you just need to pick one set of numbers and, as long as those numbers are permissible (i.e. follow the rules given), you'll get the right answer to the question.

Since y is a fraction, 1/2 makes sense, since it's usually the easier fraction to work with.

x is negative, so you certainly can pick x=-1 (since that's also a fairly simple number), but you could also pick x=-10 or -37 or -43.228 if you think that's going to make the math simpler.

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

Kaplan Exclusive: The Official Test Day Experience | Ready to Take a Free Practice Test? | Kaplan/Beat the GMAT Member Discount
BTG100 for $100 off a full course

Like this post

mitzwillrockgmat: Master | Next Rank: 500 Posts; Posts: 124; Joined: Wed May 19, 2010 10:20 pm; Thanked: 3 times; GMAT Score:1100

by mitzwillrockgmat » Thu May 20, 2010 8:32 pm

Stuart Kovinsky wrote:
mitzwillrockgmat wrote:If x < 0 and 0 < y < 1, which of the following has the greatest value?

A. x2
B. (xy)^2
C. (x/y )^2
D. x^2/y
E. x^2y

Yes, i know this is an easy question & the answer is c if you use values x = -1 & y=1/2 but my question is, in less than a minute how can i reach this solution? i'm timing mysle fand i ended up spending 5 minutes plugging in values before reaching this combination!

So should i just simply keep values like -1 , 1/2 etc in mind so that i can plug them in quickly or is there another approach to this?

Also other than -1, 1/2 what are other values are good for testing?

Thank you!!

Hi,

the question is "which of the following has the greatest value" - there's no wriggle room, so no matter which numbers you pick, the same choice will be the biggest.

In other words, you just need to pick one set of numbers and, as long as those numbers are permissible (i.e. follow the rules given), you'll get the right answer to the question.

Since y is a fraction, 1/2 makes sense, since it's usually the easier fraction to work with.

x is negative, so you certainly can pick x=-1 (since that's also a fairly simple number), but you could also pick x=-10 or -37 or -43.228 if you think that's going to make the math simpler.

thanks all!

Like this post

artistocrat: Master | Next Rank: 500 Posts; Posts: 152; Joined: Wed Mar 12, 2008 4:36 pmFollowed by: 2 members; Thanked: 8 times

by artistocrat » Mon Feb 21, 2011 1:04 pm

Just my two cents but I happened to notice that every single answer choice has x^2, so in light of this x^2 is a constant, and hence, irrelevant. The reason its irrelevant is that even if x is negative, x^2 will always be positive, so it doesn't matter what value you use to plug in for x. It simply doesn't matter. so the question can be rephrased in this way:

(A) 1
(B) y^2
(C) 1/(Y^2)
(D) 1/Y
(E) Y

Clearly C wins.

Good luck!

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

559 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