It is currently 18 Nov 2017, 14:52

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

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

simple probability quest

  post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
Manager
Manager
avatar
Joined: 14 Dec 2004
Posts: 116

Kudos [?]: 70 [0], given: 0

simple probability quest [#permalink]

Show Tags

New post 04 Mar 2005, 05:27
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

Hi,

I can't get this simple probability question right. I just have the answers, no explanation. Here it is:

Two marbles are drawn in succession from a box containing 10red, 30white, 20blue, and 15 orange marbles, replacements being made after each drawing.

Find the probability that:
(1) They are either red or white or both (red and white)
(2) at most one is red
(3) only one is red

Answers are:
(1) 64/225
(2) 221/225
(3) 52/225

Kudos [?]: 70 [0], given: 0

SVP
SVP
User avatar
Joined: 03 Jan 2005
Posts: 2228

Kudos [?]: 385 [0], given: 0

Re: simple probability quest [#permalink]

Show Tags

New post 04 Mar 2005, 08:04
(1) They are either red or white or both (red and white)
40/75*40/75=8/15*8/15=64/225

(2) at most one is red
Doesn't this mean both cannot be red?
1-10/75*10/75=1-2/15*2/15=1-4/225=221/225

(3) only one is red
First one is red, or the second one is red
(10/75*65/75)*2 = 2/15*13/15*2=52/225

Kudos [?]: 385 [0], given: 0

Director
Director
avatar
Joined: 27 Dec 2004
Posts: 894

Kudos [?]: 54 [0], given: 0

 [#permalink]

Show Tags

New post 04 Mar 2005, 08:17
what is wrong with this for (1)?

(10/75 * 10/75) + (30/75 * 30/75) + (10/75 * 30/75)

(R AND R) (W AND W) (R AND W)

= 52/225

Kudos [?]: 54 [0], given: 0

SVP
SVP
User avatar
Joined: 03 Jan 2005
Posts: 2228

Kudos [?]: 385 [0], given: 0

 [#permalink]

Show Tags

New post 04 Mar 2005, 08:35
You are missing (W and R).
It should be:
(10/75 * 10/75) + (30/75 * 30/75) + (10/75 * 30/75)*2
= 64/225

Kudos [?]: 385 [0], given: 0

Director
Director
avatar
Joined: 27 Dec 2004
Posts: 894

Kudos [?]: 54 [0], given: 0

 [#permalink]

Show Tags

New post 04 Mar 2005, 08:37
Do you mean W and R is not the same as R and W?

Kudos [?]: 54 [0], given: 0

SVP
SVP
User avatar
Joined: 03 Jan 2005
Posts: 2228

Kudos [?]: 385 [0], given: 0

 [#permalink]

Show Tags

New post 04 Mar 2005, 08:41
Exactly. Orders matter this time. First draw is R and second is W is a different outcome from first draw is W and second is R.

Kudos [?]: 385 [0], given: 0

Intern
Intern
avatar
Joined: 02 Mar 2005
Posts: 1

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

 [#permalink]

Show Tags

New post 04 Mar 2005, 08:42
Folaa3 wrote:
what is wrong with this for (1)?

(10/75 * 10/75) + (30/75 * 30/75) + (10/75 * 30/75)

(R AND R) (W AND W) (R AND W)

= 52/225



You forgot the (W and R) possibility, so you should add 12/225.

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

Manager
Manager
avatar
Joined: 25 Oct 2004
Posts: 246

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

 [#permalink]

Show Tags

New post 04 Mar 2005, 09:20
(I) Both are red or both are white or one white the other red:

10/75*10/75 + 30/75*30/75 + 10/75* 30/75 + 30/75*10/75 = 64/225

(II) at most one is red:
(a) none is red
65/75*65/75= 4225/5625
(b) only one is red:
When it is RW :
10/75*65/75= 650/5625
When it is WR "
65/75 *10/75 = 650/5625

Adding the above prob = 221/225

(III)Only one is red:
RW: 10/75*65/75 = 650/5625
WR: 65/75*10/75 = 650/5625

Adding the above prob =52/225

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

  [#permalink] 04 Mar 2005, 09:20
Display posts from previous: Sort by

simple probability quest

  post reply Question banks Downloads My Bookmarks Reviews Important topics  

Moderator: chetan2u



GMAT Club MBA Forum Home| About| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

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

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.