A Coin Game (Posted on 2004-05-20)

	Submitted by Brian Smith
Rating: 3.5000 (4 votes)
Solution:	(Hide)
1/2 Compare Alex's 20 flips to Bert's first 20 spins. By symmetry, there is (a) a X chance that Alex gets more heads, (b) a X chance that Bert gets more heads, and (c) a 1-2X chance that they tie. If Bert's 21st spin is a head, then he wins all of (b) and (c), but none of (a); the best he can get from (a) is a tie, which Alex wins. If Bert's 21st spin is a tail, then he wins all of (c), but none of (a) or (b). Bert's overall chance of winning is (1/2)(X + (1-2X)) + (1/2)(X) = 1/2.

	Subject	Author	Date
	Solution	Math Man	2018-06-29 21:16:25
	Puzzle Solution	K Sengupta	2009-02-26 15:31:58
	No Subject	CharleyA.	2007-04-19 12:47:43
	answer	K Sengupta	2007-03-09 05:07:21
	Probability under a microscope	Carlos Da Peanut	2004-05-27 22:20:09
	re: Solution	Popstar Dave	2004-05-23 02:59:13
	Solution	Gururaj	2004-05-22 04:31:27
	re: Assuming .5 solution	Charlie	2004-05-20 22:12:41
	re: flip vs spin	Iain	2004-05-20 17:12:04
	Assuming .5 solution	Jer	2004-05-20 14:19:31
	Answer	Oskar	2004-05-20 14:17:57
	flip vs spin	Jer	2004-05-20 14:08:34