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(Note: r is the probability of obtaining heads when tossing the same coin once.) Plot of the probability density f(r | H = 7, T = 3) = 1320 r 7 (1 − r) 3 with r ranging from 0 to 1. The probability for an unbiased coin (defined for this purpose as one whose probability of coming down heads is somewhere between 45% and 55%)
In probability theory and statistics, a sequence of independent Bernoulli trials with probability 1/2 of success on each trial is metaphorically called a fair coin. One for which the probability is not 1/2 is called a biased or unfair coin. In theoretical studies, the assumption that a coin is fair is often made by referring to an ideal coin.
The probability of an event is a number between 0 and 1; the larger the probability, the more likely an event is to occur. [note 1] [1] [2] This number is often expressed as a percentage (%), ranging from 0% to 100%. A simple example is the tossing of a fair (unbiased) coin.
Coin grading [1] is the process of determining the grade or condition of a coin, one of the key factors in determining its collectible value. A coin's grade is generally determined by six criteria: strike, preservation, luster, color, attractiveness, and occasionally the country/state in which it was minted. Several grading systems have been ...
If a fair coin is flipped 21 times, the probability of 21 heads is 1 in 2,097,152. The probability of flipping a head after having already flipped 20 heads in a row is 1 / 2 . Assuming a fair coin: The probability of 20 heads, then 1 tail is 0.5 20 × 0.5 = 0.5 21; The probability of 20 heads, then 1 head is 0.5 20 × 0.5 = 0.5 21
The probability of 8 or more positives among 10 deer or 2 or fewer positives among 10 deer is the same as the probability of 8 or more heads or 2 or fewer heads in 10 flips of a fair coin. The probabilities can be calculated using the binomial test , with the probability of heads = probability of tails = 0.5.
Identically distributed: Regardless of whether the coin is fair (with a probability of 1/2 for heads) or biased, as long as the same coin is used for each flip, the probability of getting heads remains consistent across all flips. Such a sequence of i.i.d. variables is also called a Bernoulli process.
The Sheldon Coin Grading Scale is a 70-point coin grading scale used in the numismatic assessment of a coin's quality. The American Numismatic Association based its Official ANA Grading Standards in large part on the Sheldon scale. [1] The scale was created by William Herbert Sheldon.
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