BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Probability question

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Junior | Next Rank: 30 Posts
Posts: 26
Joined: Sun May 01, 2011 2:31 pm

Probability question

by Spartacus2000 » Fri Jun 17, 2011 6:40 am
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 that the marble chosen will be white?

(1) r/b + w > w/b + r
(2) b - w > r

What is the best way to tackle this?
Top
Source: — Data Sufficiency |
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pm
Location: New York, NY
Thanked: 13060 times
Followed by:1906 members
GMAT Score:790

by GMATGuruNY » Fri Jun 17, 2011 6:45 am
Spartacus2000 wrote: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 that the marble chosen will be white?

(1) r/b + w > w/b + r
(2) b - w > r

What is the best way to tackle this?
Check here for my solution, which involves almost no math:

https://www.beatthegmat.com/gmatprep-pro ... 84566.html
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
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 3835
Joined: Fri Apr 02, 2010 10:00 pm
Location: Milpitas, CA
Thanked: 1854 times
Followed by:523 members
GMAT Score:770

by Anurag@Gurome » Fri Jun 17, 2011 6:46 am
Refer to the post here : https://www.beatthegmat.com/post334175.html#334175
Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)

Join Our Facebook Groups
GMAT with Gurome
https://www.facebook.com/groups/272466352793633/
Admissions with Gurome
https://www.facebook.com/groups/461459690536574/
Career Advising with Gurome
https://www.facebook.com/groups/360435787349781/
Top
Legendary Member
Posts: 1448
Joined: Tue May 17, 2011 9:55 am
Location: India
Thanked: 375 times
Followed by:53 members

by Frankenstein » Fri Jun 17, 2011 6:47 am
Hi,
For the probability of picking red to be greater than that of white, we need to check : is r > w
From(1):
r/b + w > w/b + r
Adding 1 on both sides we get (b+r+w)/(b+w) > (b+r+w)/(b+r). As all are positives quantities,
this means 1/(b+w) > 1/(b+r) i.e. b+r>b+w. So, r>w
Sufficient

From(2): b-w>r
cannot establish which of r ,w is greater
Not sufficient

Hence, A
Cheers!

Things are not what they appear to be... nor are they otherwise
Top
User avatar
Master | Next Rank: 500 Posts
Posts: 461
Joined: Tue May 10, 2011 9:09 am
Location: pune
Thanked: 36 times
Followed by:3 members

by amit2k9 » Fri Jun 17, 2011 6:54 am
r/(b+w+r) > w/(b+w+r) = (r-w)/(b+w+r) > 0 ?

a (r-w)/b > r-w this is possible only if (r-w)/b < 0 and r-w < 0
in the negative side -1/k < -1 is the correlation.

A sufficient.

b b > r+w not sufficient.

Hence A it is.
For Understanding Sustainability,Green Businesses and Social Entrepreneurship visit -https://aamthoughts.blocked/
(Featured Best Green Site Worldwide-https://bloggers.com/green/popular/page2)
Top
Post new topic Post Reply
• Page 1 of 1