If you need a random number.

If I need a random number, I use 4. It's the result of a dice throw I did three years ago, so it must be random, right?
 
I fancy boys said:
is that true? i always thought the chance of the same element each time decreased as the number of trials increased, like a binomial distribution
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Nope. Say you're rolling a dice. The first time, you have a 1 in 6 chance of getting a 4. Roll it again, you still have a 1 in 6 chance of getting a 4. Doesn't matter how many times you roll it, you have the same chance of getting a 4 every time.

Of course, it's still very unlikely you'll get "4, 4, 4, 4, 4" compared to getting a bunch of different numbers, but if you compare a specific sequence of numbers, like "6, 1, 4, 2, 5", the chances are exactly the same.
 
I fancy boys said:
is that true? i always thought the chance of the same element each time decreased as the number of trials increased, like a binomial distribution
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As D D Danneh said, the probability of rolling a specific number on a die is always 1/6, so the probability of rolling a specific sequence decreases by a factor of 6 with each successive roll of the die, regardless of which numbers you want to roll. This is simply because die rolls follow a uniform distribution (i.e. they're unbiased).
 
Inquisitor said:
As D D Danneh said, the probability of rolling a specific number on a die is always 1/6, so the probability of rolling a specific sequence decreases by a factor of 6 with each successive roll of the die, regardless of which numbers you want to roll. This is simply because die rolls follow a uniform distribution (i.e. they're unbiased).
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ahh i understand :) i was thinking of successive trials, yeah i see now, each specific trial shall have the same probability, thankyou
 
Don't random number generators actually use the digits of pi? Or do random number generators actually exist where they don't have to use a string of numbers which it knows to be random.
 
D D Danneh said:
Nope. Say you're rolling a dice. The first time, you have a 1 in 6 chance of getting a 4. Roll it again, you still have a 1 in 6 chance of getting a 4. Doesn't matter how many times you roll it, you have the same chance of getting a 4 every time.

Of course, it's still very unlikely you'll get "4, 4, 4, 4, 4" compared to getting a bunch of different numbers, but if you compare a specific sequence of numbers, like "6, 1, 4, 2, 5", the chances are exactly the same.
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That reminds me of the guy on here who said: "If you're in a helicopter crash once then you can't be in a second - it's not possible."

But yeah, as others have said - given one number in the list (assuming independant probabilities) then getting the same number again is no more or less likely than any other number, and any specific sequence is equally as likely as any other specific sequence.

And random number: 393457

My favourite number = 47, though. Can't beat a 47.

ghost101 said:
Don't random number generators actually use the digits of pi? Or do random number generators actually exist where they don't have to use a string of numbers which it knows to be random.
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That depends on how the number is generated. As mentioned above, atmospheric noise can produce very good approximations to noise, as can nuclear decay and thermal noise, as well as lava lamps. Any algorithm though, by definition, must not be random, otherwise the accuracy of its "random-ness" cannot be verified.
 
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