Author
| Message |
|---|
|
|
If you flip a coin 20 times and it comes up heads all 20 times....Now on the 21st flip what are the odds of the coin coming up heads.......................50%............... first set of data does not influance the 21st flip....
|
|
|
Odie,
How many times have youu gone outside? Lets say 3 times per day. Roughly 1000 times a year. If you have been struck by lightning 500 times in the past year than you have a 50% chance of being struck the next time you go outside.
Suppose you have a blue die and a red die. What are the chances of rolling a 7. Well either you roll a 7 or you dont. But the chance of rolling a 7 is not 50%. There are six possible outcomes if you roll one die. For every roll of the first die there are 6 possible outcomes when you roll the second. That means there are 36 different results. Here I consider a blue 4 and a red 2 to be a different outcome than a red 4 and a blue 2.
No matter what the roll of the first die there is one and only one roll of the second that will give you 7. This means there are 6 ways to get 7 when you roll 2 dice. 36 total outcomes the possibility of rolling a 7 is 6/36 or 1/6.
When playing cards will the next card be the 5 of clubs. Either it will or it will not. but the chance of the next card being a 5 of clubs is not 50% it is 1/52.
|
|
|
mobe
for the coin flip you know the chance of heads is 50%. Supose you dont know that. Then you would do an experiment. You would flip a coin 1000 times. You might get 502 heads. We kow that if the chance on each trial is 50% the the distribution will be a guassian centered at 50%. It turns out that this guassian function is narrow. But not so narrow as to make 502 a tremondous surprise. So You gues that the chance of getting heads is between 49% and 53%. You repaet this experiment a 1000 times and discover that 1 million coin flips cuases your fingers to cramp. Oops. You find that 499 occurs often. 500 occurs often. But all you results are between 485 and 515. You conclude that the probability is between 49.99% and 50.01%
By the way the chance of getting heads 20 heads out of 20 flips is 0.5^20= 9.5 x10^-7. slightly less than one time in a million. However if you flipped a coin 20 times and got heads 20 times and that is all you knew aboout coin flips you would conclude that the chance of getting tails is far less than 1 in a 1000
|
|
|
Yes, the coin flip is a bad example to use here. Each flip is an independent event and assuming that the coin is perfectly balanced, the odds of flipping heads is exactly 50%.
However as Phys pointed out, the odds of flipping 500 heads from 1000 coin flips is quite small. The sum of one small slice of the curve divided by the entire area of the curve. Less that a percent I think.
This sort of scenario should not be compared to the original question where each potential event is related in many ways.
|
|
|
| If you flip a coin 20 times and it comes up heads all 20 times... |
Good grief, Mobe, that's not a legit coin! I'd say the odds are pretty good it will be heads again. 
|
| Previous 1 2 3 4 Next |
