Algebra Expressions- Not so simple!

Expert replies

Kemmy G: Junior | Next Rank: 30 Posts; Posts: 19; Joined: Wed Apr 06, 2011 8:50 amFollowed by: 1 member

by Kemmy G » Wed Jun 15, 2011 12:39 pm

Can someone PLEASE explain question 148 of the 12 ed. OG quant section?
[x/x+y](10)+[y/x+y](20)= k.
What could be the value of k?

I've studied the explanation in the OG answer question and am still as stumped as ever. Can someone PLEASE explain it step by step, so it's really easy to follow and grasp?

Thanks,

Like this post

Source: Beat The GMAT — Problem Solving | Wed Jun 15, 2011 12:39 pm

Frankenstein: Legendary Member; Posts: 1448; Joined: Tue May 17, 2011 9:55 amFollowed by: 53 members; Location: India; Thanked: 375 times

by Frankenstein » Wed Jun 15, 2011 1:23 pm

Hi,
Please post the complete question, including options. You haven't even posted the condition x<y and
x,y are positive numbers.

[x/x+y](10)+[y/x+y](20) = (10x+20y)/(x+y) = [10(x+y)+10y]/(x+y)
= 10[1 + (y/x+y)]
Given x < y => x+y < y+y
So, x+y < 2y => y/(x+y) > 1/2
and y/(x+y) < 1
So, 10[1 + (y/x+y)] > 10[1+ (1/2)] & 10[1 + (y/x+y)] < 10[1+ 1]
So, [x/x+y](10)+[y/x+y](20) > 15 & [x/x+y](10)+[y/x+y](20) < 20
So, any value between 15 and 20 could be the value of k.

Last edited by Frankenstein on Wed Jun 15, 2011 1:28 pm, edited 1 time in total.

Cheers!

Things are not what they appear to be... nor are they otherwise

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 Jun 15, 2011 1:27 pm

i'll try without looking up an official explanation
with our conditions given x<y and x,y,k>0 we set k=(10x+20y)/(x+y) and this is equivalent to 10+10y/(x+y); because 10y/(x+y) is more than 10/2 {x<y, hence x+y<2y} our answer can be in the interval (greater than 15 and less than 20), so it's d

Kemmy G wrote:Can someone PLEASE explain question 148 of the 12 ed. OG quant section?
[x/x+y](10)+[y/x+y](20)= k.
What could be the value of k?

I've studied the explanation in the OG answer question and am still as stumped as ever. Can someone PLEASE explain it step by step, so it's really easy to follow and grasp?

Thanks,

Success doesn't come overnight!

Like this post

GMATGuruNY: GMAT Instructor; Posts: 15539; Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members; Location: New York, NY; Thanked: 13060 times; GMAT Score:790

by GMATGuruNY » Wed Jun 15, 2011 2:17 pm

I posted an easy solution here: https://www.beatthegmat.com/tough-algebr ... tml#292229

Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3

Like this post

Kemmy G: Junior | Next Rank: 30 Posts; Posts: 19; Joined: Wed Apr 06, 2011 8:50 amFollowed by: 1 member

by Kemmy G » Tue Aug 02, 2011 3:28 am

Thank you so much guys, especially GMATGuruNY!!!

I thought I would receive alerts in my email box whenever anyone replied to my post, and since none came, I simply assumed the question wasn't answered. Will have to improve on checking BTG more regularly,

. Thanks again everyone.

Off to study and understand the question again!

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