Math Help Forum

Math Help Forum Feed Site Feed

Go Back   Math Help Forum > University Math Help > Discrete Mathematics, Set Theory and Logic
Reply
 
Thread Tools Display Modes
  #1  
Old May 1st, 2008, 11:55 AM
Junior Member
 
Join Date: Apr 2008
Posts: 56
Country:
Thanks: 3
Thanked 0 Times in 0 Posts
ccdelia7 is on a distinguished road
Default 30.8 - Events and Probability of dice

Three dice are rolled. What is the probability that the sum of the numbers showing is even? Explain.

-I had a quiz with this question and I got it wrong. I assume I had an improper sample space??

Thanks
Reply With Quote
Advertisement
 
  #2  
Old May 1st, 2008, 12:07 PM
MHF Contributor
 
Join Date: Apr 2008
Posts: 1,046
Country:
Thanks: 18
Thanked 431 Times in 419 Posts
icemanfan is just really niceicemanfan is just really niceicemanfan is just really niceicemanfan is just really niceicemanfan is just really nice
Default

Quote:
Originally Posted by ccdelia7 View Post
Three dice are rolled. What is the probability that the sum of the numbers showing is even? Explain.

-I had a quiz with this question and I got it wrong. I assume I had an improper sample space??

Thanks
Three fair, six-sided dice? The answer should be 1/2, I think.
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Reply With Quote
  #3  
Old May 1st, 2008, 12:17 PM
CaptainBlack's Avatar
Grand Panjandrum
 
Join Date: Nov 2005
Location: South of England
Posts: 12,271
Country:
Thanks: 777
Thanked 3,995 Times in 3,223 Posts
CaptainBlack has a reputation beyond reputeCaptainBlack has a reputation beyond reputeCaptainBlack has a reputation beyond reputeCaptainBlack has a reputation beyond reputeCaptainBlack has a reputation beyond reputeCaptainBlack has a reputation beyond reputeCaptainBlack has a reputation beyond reputeCaptainBlack has a reputation beyond reputeCaptainBlack has a reputation beyond reputeCaptainBlack has a reputation beyond reputeCaptainBlack has a reputation beyond repute
Default

Quote:
Originally Posted by ccdelia7 View Post
Three dice are rolled. What is the probability that the sum of the numbers showing is even? Explain.

-I had a quiz with this question and I got it wrong. I assume I had an improper sample space??

Thanks
The sum is even when you have exactly three even or exactly one even, the number of evens
is binomial \sim B(3,0.5), so:

p(even\ sum)=b(1;3,0.5)+b(3,3,0.5)=3 \times 0.5^3 + 0.5^3=0.5

RonL
__________________
Truth does not change because it is, or is not, believed by a majority of the people.

Giordano Bruno
Reply With Quote
  #4  
Old May 1st, 2008, 12:17 PM
Junior Member
 
Join Date: Apr 2008
Posts: 56
Country:
Thanks: 3
Thanked 0 Times in 0 Posts
ccdelia7 is on a distinguished road
Smile

I assume you're right, that the odds are 1/2 because if you think about it,

- Any even number added to any even number added to any even number is even.

- Any number added to any even number added to any odd number is odd

-Any odd number added to any odd number added to any odd number is odd.

- Any odd number added to any odd number added to any even number is even.


Are there any other cases that I'm neglecting?? That's where I have the problem!
Reply With Quote
  #5  
Old May 1st, 2008, 12:19 PM
Isomorphism's Avatar
Wesnoth Rookie

 
Join Date: Dec 2007
Location: IISc, Bangalore
Posts: 1,368
Country:
Thanks: 450
Thanked 673 Times in 563 Posts
Isomorphism is a splendid one to beholdIsomorphism is a splendid one to beholdIsomorphism is a splendid one to beholdIsomorphism is a splendid one to beholdIsomorphism is a splendid one to beholdIsomorphism is a splendid one to beholdIsomorphism is a splendid one to behold
Default

Quote:
Originally Posted by ccdelia7 View Post
Three dice are rolled. What is the probability that the sum of the numbers showing is even? Explain.
Quote:
Originally Posted by icemanfan View Post
Three fair, six-sided dice? The answer should be 1/2, I think.
Yes... icemanfan is right
Quote:
Originally Posted by ccdelia7 View Post
-I had a quiz with this question and I got it wrong. I assume I had an improper sample space??
Thanks
What?!!You listed(or even thought of trying to list) all the 108 possible throws that gave an even sum?

To prove the answer is 0.5, consider the fact that only throws which have all even numbers and the ones with 1 odd number gives a even sum...

EDIT: Yes, you are right. I was trying to explain the very thing you wrote...What did you do in the quiz??
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


Algebra is the offer made by the devil to the mathematician. The devil says: `I will give you this powerful machine, it will answer any question you like. All you need to do is give me your soul: give up geometry and you will have this marvellous machine.'
—Michael Atiyah
Reply With Quote
  #6  
Old May 1st, 2008, 01:56 PM
Junior Member
 
Join Date: Apr 2008
Posts: 56
Country:
Thanks: 3
Thanked 0 Times in 0 Posts
ccdelia7 is on a distinguished road
Smile thanks

No i was just trying to think of the probability logically, and it seemed as though the chances would be higher than 1/2, like 3/2. But i see now, what the real approach should be.

Thanks to everyone!
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off
Forum Jump


All times are GMT -7. The time now is 11:58 AM.


Powered by vBulletin® Version 3.7.3
Copyright ©2000 - 2010, Jelsoft Enterprises Ltd.
SEO by vBSEO 3.2.0 ©2008, Crawlability, Inc.
©2005 - 2009 Math Help Forum


Math Help Forum is a community of maths forums with an emphasis on maths help in all levels of mathematics.
Register to post your math questions or just hang out and try some of our math games or visit the arcade.