GMAT prep2 Probability

Expert replies

Previous Topic Next Topic

rahulg83: Legendary Member; Posts: 575; Joined: Tue Nov 04, 2008 2:58 amFollowed by: 4 members; Location: India; Thanked: 18 times; GMAT Score:710

by rahulg83 » Mon Jun 29, 2009 3:24 am

Like this post

Source: Beat The GMAT — Problem Solving | Mon Jun 29, 2009 3:24 am

Morgoth: Master | Next Rank: 500 Posts; Posts: 316; Joined: Mon Sep 22, 2008 12:04 amFollowed by: 1 member; Thanked: 36 times

by Morgoth » Mon Jun 29, 2009 8:43 am

question stem: r > w ?

Statement I

r/(b+w) > w/(b+r)

Assume, b=0

r/w > w/r

r^2 > w^2

r > w, since balls cannot be in negative.

Another way of doing this will be by picking numbers, the only way this equation will be satisfied, when r > w.

if, r = 6, w=3 , b=1

r/(b+w) > w/(b+r)

6/4 > 3/7

if, r = 4, w=5, b=1

r/(b+w) > w/(b+r)

4/6 > 5/5

Therefore, r > w. Sufficient.

Statement II

b - w > r

We need to know individual values of b, w and r

if b=12, w=5, r= 6

12 -5 > 6

7> 6

but, r>w

if b=12, w=7, r=4

12 - 7 > 4

5 > 4

but, r < w

Insufficient.

Hence A.

Hope this helps.

Like this post

ghacker: Master | Next Rank: 500 Posts; Posts: 148; Joined: Wed Jun 03, 2009 8:04 pmFollowed by: 1 member; Thanked: 18 times

by ghacker » Thu Jul 02, 2009 8:41 am

This is a simple question if you know a definition of probability

P(red) = Red / Total

we are asked whether P(red) > P(white)

Statement I : r/b+w > w/b+r

r/b+w +1 > w/b+r +1

r+b+w /b+w > w+b+r/b+r

b+r > b+w

r > w , hence r/b+w+r > w/b+w+r or P(r)> P(w)

Hence statement I is sufficient

Statement II : b-w > r -------------> b > w+r insufficient

hence Ans = A

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