GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 21 Oct 2019, 23:37

Close

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Close

Request Expert Reply

Confirm Cancel

Box 1 contains 3 red and 5 white balls, while box 2 contains 4 red and

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Find Similar Topics 
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 58404
Box 1 contains 3 red and 5 white balls, while box 2 contains 4 red and  [#permalink]

Show Tags

New post 29 Jan 2019, 03:02
00:00
A
B
C
D
E

Difficulty:

  35% (medium)

Question Stats:

67% (02:21) correct 33% (02:18) wrong based on 32 sessions

HideShow timer Statistics

Box 1 contains 3 red and 5 white balls, while box 2 contains 4 red and 2 white balls. A ball is chosen at random from the first box and placed in the second box without observing its color. Then the ball is drawn from the second box. Find the probability that it is white.

A. 2/7
B. 3/8
C. 3/7
D. 4/7
E. 5/8

_________________
CEO
CEO
User avatar
D
Status: GMATINSIGHT Tutor
Joined: 08 Jul 2010
Posts: 2978
Location: India
GMAT: INSIGHT
Schools: Darden '21
WE: Education (Education)
Reviews Badge
Box 1 contains 3 red and 5 white balls, while box 2 contains 4 red and  [#permalink]

Show Tags

New post 29 Jan 2019, 03:58
1
Bunuel wrote:
Box 1 contains 3 red and 5 white balls, while box 2 contains 4 red and 2 white balls. A ball is chosen at random from the first box and placed in the second box without observing its color. Then the ball is drawn from the second box. Find the probability that it is white.

A. 2/7
B. 3/8
C. 3/7
D. 4/7
E. 5/8


Probability of Last ball chosen white = Total White balls in Box 2 / Total balls in Box 2

Box 1: 3 red and 5 white balls
Box 2: 4 red and 2 white balls

Case 1: Ball chosen Box 1 is White and then Ball chosen from Box 2 is White
Favourable Probability = Probability of chosen ball white in box 1 * Probability of chosen ball white from box 2

i.e. Favourable Probability = (5/8)*(3/7)


Case 2: Ball chosen Box 1 is Red and then Ball chosen from Box 2 is White
Favourable Probability = Probability of chosen ball Red in box 1 * Probability of chosen ball white from box 2

i.e. Favourable Probability = (3/8)*(2/7)


Total Favourable Probability = Probability of case 1+ Probability of Case 2

i.e. Required Probability = (5/8)*(3/7) + (3/8)*(2/7) = (15+6)/56 = 21/56 = 3/8

Answer: Option B
_________________
Prosper!!!
GMATinsight
Bhoopendra Singh and Dr.Sushma Jha
e-mail: info@GMATinsight.com I Call us : +91-9999687183 / 9891333772
Online One-on-One Skype based classes and Classroom Coaching in South and West Delhi
http://www.GMATinsight.com/testimonials.html

ACCESS FREE GMAT TESTS HERE:22 ONLINE FREE (FULL LENGTH) GMAT CAT (PRACTICE TESTS) LINK COLLECTION
GMAT Club Legend
GMAT Club Legend
User avatar
D
Joined: 18 Aug 2017
Posts: 5027
Location: India
Concentration: Sustainability, Marketing
GPA: 4
WE: Marketing (Energy and Utilities)
GMAT ToolKit User Premium Member
Re: Box 1 contains 3 red and 5 white balls, while box 2 contains 4 red and  [#permalink]

Show Tags

New post 29 Jan 2019, 04:09
Bunuel wrote:
Box 1 contains 3 red and 5 white balls, while box 2 contains 4 red and 2 white balls. A ball is chosen at random from the first box and placed in the second box without observing its color. Then the ball is drawn from the second box. Find the probability that it is white.

A. 2/7
B. 3/8
C. 3/7
D. 4/7
E. 5/8


we can solve it considering two cases

case 1 : only white balls are chosen from box 1 and is transferred to box 2
P ( white ) ;5/8 * 3/7

case 2: red ball is chosen from box 1 and is transferred to box 2
P (white ) ; 3/8 * 2/7
5/8 * 3/7 + 3/8 * 2/7

15+6/56 = 21/56 ; 3/8
IMO B
GMAT Club Bot
Re: Box 1 contains 3 red and 5 white balls, while box 2 contains 4 red and   [#permalink] 29 Jan 2019, 04:09
Display posts from previous: Sort by

Box 1 contains 3 red and 5 white balls, while box 2 contains 4 red and

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  





Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne