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Coin flipping, coin tossing, or heads or tails is the practice of throwing a coin in the air and checking which side is showing when it lands, in order to randomly choose between two alternatives. It is a form of sortition which inherently has two possible outcomes.
The probability of 20 heads, then 1 head is 0.5 20 × 0.5 = 0.5 21; The probability of getting 20 heads then 1 tail, and the probability of getting 20 heads then another head are both 1 in 2,097,152. When flipping a fair coin 21 times, the outcome is equally likely to be 21 heads as 20 heads and then 1 tail.
A test is performed by tossing the coin N times and noting the observed numbers of heads, h, and tails, t. The symbols H and T represent more generalised variables expressing the numbers of heads and tails respectively that might have been observed in the experiment. Thus N = H + T = h + t.
A simple example is the tossing of a fair (unbiased) coin. Since the coin is fair, the two outcomes ("heads" and "tails") are both equally probable; the probability of "heads" equals the probability of "tails"; and since no other outcomes are possible, the probability of either "heads" or "tails" is 1/2 (which could also be written as 0.5 or 50%).
Using for heads and for tails, the sample space of a coin is defined as: Ω = { H , T } {\displaystyle \Omega =\{H,T\}} The event space for a coin includes all sets of outcomes from the sample space which can be assigned a probability, which is the full power set 2 Ω {\displaystyle 2^{\Omega }} .
In the heads scenario, Sleeping Beauty would spend her wager amount one time, and receive 1 money for being correct. In the tails scenario, she would spend her wager amount twice, and receive nothing. Her expected value is therefore to gain 0.5 but also lose 1.5 times her wager, thus she should break even if her wager is 1/3.
The outer coin makes two rotations rolling once around the inner coin. The path of a single point on the edge of the moving coin is a cardioid.. The coin rotation paradox is the counter-intuitive math problem that, when one coin is rolled around the rim of another coin of equal size, the moving coin completes not one but two full rotations after going all the way around the stationary coin ...
Spinner spins a pair of heads before a pair of tails or odding out. Single Tail 3.125% 1–1 Spinner spins a pair of tails before a pair of heads or odding out. 5 Odds 9.375% 28–1 Spinner spins five odds in a row ("odding out") before either a pair of heads or a pair of tails. Spinner's Bet 3.400% 15–2 Only available to the current spinner.