Standard deviation of a dice roll?

In summary, to find the exact standard deviation of a roll of a 50-sided die, you can use the formulas for the first and second moments, which are (n+1)/2 and (n+1)(2n+1)/6 respectively. Another alternative formula is \mbox{var}(X)=E[X^2]-E[X]^2, which can be found on Wikipedia. Simply plug in the values for n and use the formulas to calculate the standard deviation.
  • #1
moonman239
282
0
Let's say I have a big, 50-sided die, with values ranging from 1-50. I want to find the exact standard deviation of the dice roll by hand. I would like to avoid subtracting the mean from each possible value, if at all possible.

How do I do that?
 
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  • #2
The most direct way is to get the averages of the numbers (first moment) and of the squares (second moment). The variance is the second moment minus the square of the first moment. The moments are (n+1)/2 and (n+1)(2n+1)/6 assuming a fair die. (Your n=50).
 
  • #3
An alternative formula for the variance (the square of the s.d.) is [tex]\mbox{var}(X)=E[X^2]-E[X]^2[/tex]. The derivation can be found on wikipedia. Use the formulas provided by mathman above to find the value.
 
  • #4
dalcde said:
An alternative formula for the variance (the square of the s.d.) is [tex]\mbox{var}(X)=E[X^2]-E[X]^2[/tex]. The derivation can be found on wikipedia. Use the formulas provided by mathman above to find the value.
Your formula is exactly what I posted in words.
 
  • #5
Yes, but I found the word formula a bit difficult to comprehend.
 
  • #6
The variance is the second moment minus the square of the first moment.

Looks plain enough to me.
 

What is the standard deviation of a dice roll?

The standard deviation of a dice roll is a measure of how spread out the possible outcomes are from the average roll. It tells us how much the rolls vary from each other.

How is the standard deviation of a dice roll calculated?

The standard deviation of a dice roll can be calculated by taking the square root of the average of squared differences between each roll and the mean roll. This is also known as the root mean square deviation.

What does a higher standard deviation indicate in a dice roll?

A higher standard deviation in a dice roll indicates that there is more variability in the possible outcomes. This means that the rolls are more spread out and less likely to be close to the average roll.

Can the standard deviation of a dice roll be negative?

No, the standard deviation of a dice roll cannot be negative. It is always a positive value as it is a measure of distance from the mean.

How does the number of dice rolled affect the standard deviation?

The number of dice rolled does not affect the standard deviation itself, but it does affect the range of possible outcomes. The more dice that are rolled, the smaller the range of possible outcomes and the lower the standard deviation will be.

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