Find all School-related info fast with the new School-Specific MBA Forum

It is currently 31 May 2016, 21:20
GMAT Club Tests

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.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

probabilty question - picking ball

  post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
Intern
Intern
avatar
Joined: 13 Oct 2005
Posts: 5
Followers: 0

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

probabilty question - picking ball [#permalink]

Show Tags

New post 20 Dec 2005, 18:46
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

Can someone answer this please:

A box contains 100 balls, numbered from 1 to 100. If three balls are selected at random and with replacement from the box, what is the probability that the sum of the three numbers on the balls selected from the box will be odd:
Choises:

1. 1/4
2. 3/8
3. 1/2
4. 5/8
5. 3/4
Director
Director
avatar
Joined: 14 Sep 2005
Posts: 993
Location: South Korea
Followers: 2

Kudos [?]: 104 [0], given: 0

Re: probabilty question - picking ball [#permalink]

Show Tags

New post 20 Dec 2005, 19:12
When the sum of three numbers is odd, the three numbers should be

1) three odd
2) one odd, two even

Probability of picking three odd numbers
= 1/2 * 1/2 * 1/2
= 1/8

Probability of picking one odd number and two even numbers
= 1/2 * 1/2 * 1/2 * 3
= 3/8

(multiplied by 3 since there are 3 combinations - ODD, DOD, DDO)

Thus, 1/8 + 3/8 = 1/2

-------------------------------------------------------------------------------

Or, from the fact that the probability of picking an odd number and the probability of picking an even number is the same, I guess we can do the following also.

Three numbers can be as below;

1. odd, odd, odd
2. odd, odd, even
3. odd, even, odd
4. even, odd, odd
5. odd, even, even
6. even, odd, even
7. even, even, odd
8. even, even, even

There are 8 cases in total and 4 cases(1, 5, 6, 7) will yield an odd number.
Thus it's 4/8 = 1/2.

-------------------------------------------------------------------------------------

Or..what about this approach?

The probability of picking an odd or an even number is the same.

And the result of summing three numbers will always yield odd or even number. This or that. No others. So 1/2.
_________________

Auge um Auge, Zahn um Zahn :twisted: !

Intern
Intern
avatar
Joined: 13 Oct 2005
Posts: 5
Followers: 0

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

 [#permalink]

Show Tags

New post 21 Dec 2005, 12:08
Thanks. I made a mistake in the total events, I counted 9, instead of 8, so I got confused. However, is there a formulae to count this type of events.

Lets say if there were 5 balls picked up. Then this manual listing may take long. Is there a formulae in this case. n! / k! (n-k)! does not apply here, but is there any similar one for this case?.

Thanks
Veera
Senior Manager
Senior Manager
avatar
Joined: 11 Nov 2005
Posts: 328
Location: London
Followers: 1

Kudos [?]: 10 [0], given: 0

 [#permalink]

Show Tags

New post 21 Dec 2005, 16:35
  [#permalink] 21 Dec 2005, 16:35
Display posts from previous: Sort by

probabilty question - picking ball

  post reply Question banks Downloads My Bookmarks Reviews Important topics  


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

Powered by phpBB © phpBB Group and phpBB SEO

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®.