The only way to find out for sure would be to have it certified by PCGS then consign it to one of the big auction houses. After they hype the auction to the max, the bidders will determine the value. My personal pre-auction estimate would be $25,000-$30,000. Condition wouldn't mean a lot in this case since whatever it grades, it is still the first or second best example known to exist.
Then it's just as fake as the ones with heads on both sides.
No. They're all privately-made novelty items. In fact, the Mint uses dies that are "keyed" so a tails-side die cannot be put into the heads side of a press, precisely to prevent anyone from creating a real double-sided coin. Please use this site's Search feature to look for the word DOUBLE and you'll find hundreds of similar questions. double-tailed quarter has been certified as a real mint error. See related link to the Coin World article.
Two possibilities that when you flip the coin you would get heads or tails.
Your question is very vague but if we assume "rolling a 5" is rolling a five on a six sided dice then the probability of that would be 1/6 since there are 6 sides and 5 is just 1 side. Again your question is very vague but if we assume "getting tails" means getting heads or tails on a 2 sided coin then the probability of that would be 1/2 since there are 2 sides and tails is just 1 side.
The probability of getting a six on a six sided die and then getting a tails is zero. There is no tails on a die.
Flip-over double-strike.
If your talking about the faces, then there is only one head, George Washington, but if you are talking about the sides, there are two. Heads and Tails
This is a novelty or magic coin that has been altered and was not produced by the mint And has no collection value at all.
1/2 if the quarter is 'fair'.
presidchle seal
50 %
a quarter