I took a practice test the other day and I came across a few

Oldest

Best Reply

Author

Message

TAGS:

Intern

Joined: 10 Feb 2010

Posts: 3

Followers: 0

Kudos [?]: 0 [0], given: 1

I took a practice test the other day and I came across a few [#permalink]

10 Feb 2010, 12:41

00:00

Question Stats:

0% (00:00) correct

0% (00:00) wrong

based on 0 sessions

I took a practice test the other day and I came across a few DS questions that I was unable to figure out. If you know of a good way to break down these problems I would appreciate your help.

a) In the rectangular coordinate system, are the points (r,s) and (u,v) equidistant from the origin?

1) r + s = 1

2) u = 1 - r and v = 1 - s

b) A certain jar contains only B black marbles, W white marbles, and R red marbles. If one marble is to be chosen at random from the jar, is the probability that the marble chosen will be red greater than the probability than the probability that the marble chosen will be white?

1) R / B + W > W / B + R

2) B - W > R

Manager

Joined: 05 Dec 2009

Posts: 130

Followers: 2

Kudos [?]: 73 [1] , given: 0

Re: Need Help with Two Difficult GMATPrep DS Problems [#permalink]

13 Mar 2010, 20:18

This post received
KUDOS

Thanks for the explanation

GMAT Club team member

Joined: 02 Sep 2009

Posts: 11570

Followers: 1797

Kudos [?]: 9580 [0], given: 826

Re: Need Help with Two Difficult GMATPrep DS Problems [#permalink]

10 Feb 2010, 13:13

johnmayf wrote:

Hi, welcome to the Gmat Club. The questions you are asking were discussed before, below are my solutions to them from earlier topics:

First question:

Basically the question asks is r^2+s^2=u^+v^2?

(1) r+s=1, no info about u and v;

(2) u=1-r and v=1-s --> u^2+v^2=(1-r)^2+(1-s)^2=1-2r+r^2+1-2s+s^2=2-2(r+s)+ r^2+s^2. We don't know the value of 2-2(r+s), so not sufficient.

(1)+(2) r+s=1 and u^2+v^2=2-2(r+s)+ r^2+s^2 --> u^2+v^2=2-2+r^2+s^2=r^2+s^2. Sufficient.

Answer: C.

Second question:

The question is \frac{R}{R+B+W}>\frac{W}{R+B+W} true? Or is R>W true?

(1) \frac{R}{B+W} > \frac{W}{B+R} --> \frac{R}{B+W} +1> \frac{W}{B+R}+1 --> \frac{R+B+W}{B+W}> \frac{W+B+R}{B+R} --> \frac{1}{B+W}> \frac{1}{B+R} --> B+R>B+W --> R>W. Sufficient.

(2) B-W>R, not sufficient to determine whether R>W or not.

Answer: A.
_________________

PLEASE READ AND FOLLOW: 11 Rules for Posting!!!

RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory

COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. NEW!!!

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set. NEW!!!

What are GMAT Club Tests?
25 extra-hard Quant Tests

Find out what's new at GMAT Club - latest features and updates

Intern

Joined: 10 Feb 2010

Posts: 3

Followers: 0

Kudos [?]: 0 [0], given: 1

Re: Need Help with Two Difficult GMATPrep DS Problems [#permalink]

10 Feb 2010, 18:23

Thanks for the help. I'm still confused on Statement 1 of the second question. Could you point me to your previous discussion or add further insight?

Thanks.

GMAT Club team member

Joined: 02 Sep 2009

Posts: 11570

Followers: 1797

Kudos [?]: 9580 [0], given: 826

Re: Need Help with Two Difficult GMATPrep DS Problems [#permalink]

10 Feb 2010, 18:51

johnmayf wrote:

Thanks for the help. I'm still confused on Statement 1 of the second question. Could you point me to your previous discussion or add further insight?

Thanks.

OK let me offer another way for statement (1):

Given: \frac{R}{B+W} > \frac{W}{B+R} -->

Cross multiply, we can safely do this as B+W and B+R are more then zero.

We'll get R(B+R)>W(B+W) --> RB+R^2>WB+W^2 --> (R^2-W^2)+(RB-WB)>0 --> (R-W)(R+W)+B(R-W)>0 --> (R-W)(R+W+B)>0.

As R+W+B>0, the above inequality to hold true R-W must also be more then zero, so R-W>0 --> R>W.

Hope it's clear now.
_________________

Intern

Joined: 10 Feb 2010

Posts: 3

Followers: 0

Kudos [?]: 0 [0], given: 1

Re: Need Help with Two Difficult GMATPrep DS Problems [#permalink]

11 Feb 2010, 17:59

Thanks for the explanation. Very helpful.

Could anyone point me to answer explanations for more GMATPrep questions?

Thanks.

GMAT Club team member

Joined: 02 Sep 2009

Posts: 11570

Followers: 1797

Kudos [?]: 9580 [0], given: 826

Re: Need Help with Two Difficult GMATPrep DS Problems [#permalink]

11 Feb 2010, 18:12

johnmayf wrote:

Thanks for the explanation. Very helpful.

Could anyone point me to answer explanations for more GMATPrep questions?

Thanks.

On every page you can see "View tags list by forum". There you can find "Source: GmatPrep".
_________________

Senior Manager

Joined: 01 Feb 2010

Posts: 275

Followers: 1

Kudos [?]: 30 [0], given: 2

Re: Need Help with Two Difficult GMATPrep DS Problems [#permalink]

14 Mar 2010, 03:31

johnmayf wrote:

1 clearly insufficient
2: distance (1-r)^2+(1-s)^2 = 1+r^2-2r+1+s^2-2s
we can't say it is equal to r^2+s^2

combining (1-r)^2+(1-s)^2 = r^2+s^2 so C.

Manager

Joined: 05 Mar 2010

Posts: 220

Followers: 1

Kudos [?]: 15 [0], given: 8

Re: Need Help with Two Difficult GMATPrep DS Problems [#permalink]

14 Mar 2010, 04:04

Thanks for the question and explanation
_________________

Success is my Destiny

Re: Need Help with Two Difficult GMATPrep DS Problems [#permalink] 14 Mar 2010, 04:04

		Similar topics	Author	Replies	Last post
Similar Topics:		I took the gmat the other day and one of the few problems	combres	5	21 Sep 2007, 06:22
		i came across a few questions that tests the rearrangement	bmwhype2	3	11 Jan 2008, 10:44
		i came across quite a few sentences that are making me	stallone	1	03 Oct 2008, 14:29
	1	I came across on one of the forums where these questions	AtifS	13	20 Feb 2010, 05:27
		Here is one that came in a test I tooked last week: as	aljcarranza	0	08 Dec 2010, 16:48

I took a practice test the other day and I came across a few

Main navigation

GMAT Resources

Partners

MBA Resources

GMAT ® is a registered trademark of the Graduate Management Admission Council ® (GMAC ®). GMAT Club's website has not been reviewed or endorsed by GMAC.

GMAT Courses

Admissions Consulting

I took a practice test the other day and I came across a few

I took a practice test the other day and I came across a few

Main navigation

GMAT Resources

Partners

MBA Resources