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indierock82
05-01-2007, 06:04 AM
Honestly, I don't know where these ideas come from (and for that I apologize).
I was taking out a caffeinepill this morning and I happened to drop it and instead of it landing on one side, it landed standing up. I'm sure the astute ones here know where I'm going with this.

Ever since I've been a kid I've learned and recited that when flipping a coin and letting it land there's a 50-50 chance it will either result in heads or tails. But what about the fact that it could theoretically land standing up? So taking that into account it's no longer a 50-50 chance of heads or tails, rather a 49.999999-49.999999* chance. Am I correct in assuming this?

I've never seen this done, and I'm sure none of you have either. But wouldn't it be so cool and satisfying if you accomplished the feat?

* I chose that very number of nines by random, but I'm sure you guys get the point.

essell
05-01-2007, 06:17 AM
All probabilities are just human models of real life anyway. I'd think of the coin odds as "It's 50-50 for heads or tails, for all practical purposes"

There's always the odds that the aliens will take that moment to invade, mistake the coin for an actual leader / monarch and abduct it in the hope of undermining our ability to govern ourselves.

What what are the chances of that?

zut
05-01-2007, 06:21 AM
Ever since I've been a kid I've learned and recited that when flipping a coin and letting it land there's a 50-50 chance it will either result in heads or tails. But what about the fact that it could theoretically land standing up? What about it?

Depends on how you're approaching the problem. Someone could grab the coin out of the air before it lands, too. What about that? Of the coin could land in that crack between the baseboard and the shoe molding. Or it could drop into the heating vent, in which case you're in some kind of Schroedinger's cat situation until you pry open the vent and fish it out.

Point is, when we talk about flipping a coin, we simplify the problem by ignoring unlikely outcomes. We even ignore any asymmetries in the coin itself that might prejudice the outcome.

Now, if you want to include "landing on an edge" as a third outcome (or dropping behind the shoe molding, or whatever) then you can, but assigning the correct probability for such an unlikely outcome is tricky. Much easier to round off the 50/50 and be done with it.

panache45
05-01-2007, 08:58 AM
After the pill landed on its edge, did you discover that you were able to read people's minds? Or does that only work with coins?

CookingWithGas
05-01-2007, 09:04 AM
After the pill landed on its edge, did you discover that you were able to read people's minds? Or does that only work with coins?Submitted for your approval. . . . :D

Thudlow Boink
05-01-2007, 10:18 AM
On coins whose heads and tails are not identical, the odds are not necessarily exactly fifty-fifty. For example, The U.S. penny -- with Abraham Lincoln's head on one side and the Lincoln Memorial on the other -- provides a striking example of such a bias. Stand a dozen or so pennies on edge on the surface of a table. Then bang the table so that the pennies topple over. You'll find that nearly always more heads than tails are face up. Sometimes all the coins end up heads. On the other hand, spinning pennies tend to land with tails up more often than heads!(from here (http://www.sciencenews.org/pages/sn_arc97/12_13_97/mathland.htm); see also here (http://www.sciencenews.org/articles/20040228/mathtrek.asp).)

Chronos
05-01-2007, 11:37 AM
I've never seen this done, and I'm sure none of you have either.Actually, I did once see a flipped coin come up "edge". We were deciding which team would have first possession in a basketball game, or some such, and the coin landed on the gym floor, rolled on its edge to the wall, hit the wall, and stopped.
The U.S. penny -- with Abraham Lincoln's head on one side and the Lincoln Memorial on the other -- provides a striking example of such a bias. Stand a dozen or so pennies on edge on the surface of a table. Then bang the table so that the pennies topple over. You'll find that nearly always more heads than tails are face up. Sometimes all the coins end up heads. On the other hand, spinning pennies tend to land with tails up more often than heads!This may be true, but neither bumping off the edge nor spinning is the same as flipping. All US coins are close enough to 50-50 as to be indistinguishable for any practical purpose.

Sapo
05-01-2007, 07:47 PM
For the purposes of flipping a coin, what matters is that the probability of either side are the same. The probability of an "edge" is irrelevant as long as you know how to handle that unlikely case. Even if you are flipping a tuna can with a really high chance of landing on edge, all you have to do is agree to flip those again.

In RPGs, we often needed to roll d7 or d9. We just rolled a higher die (d8 or d10) and rolled again the invalid results (8 or 10).