All about flooble | fun stuff | Get a free chatterbox | Free JavaScript | Avatars    
perplexus dot info

Home > Probability
A Coin Game (Posted on 2004-05-20) Difficulty: 3 of 5
Alex flips a fair coin 20 times. Bert spins a fair coin 21 times. Bert wins if he gets more heads than Alex, else Alex wins. Note that Alex wins if there is a tie. What is the probability that Bert wins?

See The Solution Submitted by Brian Smith    
Rating: 3.5000 (4 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
Solution re: Solution | Comment 7 of 12 |
(In reply to Solution by Gururaj)

I agree with you...
I made up a full probability distribution table and the contrasted all possible outcomes.
The probability of any one outcome for Alex: 0.5^20
multiplied by the number of combinations of that many heads out of the 20 spins: (20 C x).
As for Bert: 0.5^21 and (21 C x).
It was then a matter of contrasting these against each other and summing for a total probablility of a win for each player.
The final answer... they both have a 0.5 chance of winning.
  Posted by Popstar Dave on 2004-05-23 02:59:13

Please log in:
Remember me:
Sign up! | Forgot password

Search body:
Forums (1)
Newest Problems
Random Problem
FAQ | About This Site
Site Statistics
New Comments (2)
Unsolved Problems
Top Rated Problems
This month's top
Most Commented On

Copyright © 2002 - 2019 by Animus Pactum Consulting. All rights reserved. Privacy Information