Saturday, 1 August 2015

Probability that any outcome of a dice roll happens more than X times out of Y trials



I'm trying to determine the probability that a person experiences a "lucky number" when rolling a single, fair, 6-sided dice over a set of rolls in a single trial. A "lucky number" in this case is any face of the die that occurs visibly more common than one would normally expect. If you roll a six-sided die 100 times, you expect the outcome to occur with ~16.6 results of 1, 2, 3, 4, 5, and 6 ea, on average.



For example, you roll a six-sided dice in 100 independent trials, what is the probability that the occurrence of rolling any side of the dice happens at least 33 times over the course of the 100 independent trials? It doesn't matter if the roll was 1, 2, 3, 4, 5, or 6, just that the same result happened at least 33 times out of the 100 trials.




How would I calculate this?



Thanks.


Answer



The chance that 1 comes up exactly 33 times in 100 comes from the binomial distribution. The chance of success is 16 and failure is 56 so it is {100 \choose 33}(\frac 16)^{33}(\frac 56)^{67}\approx 0.00003 If we sum from 33 to 100 we get the chance of at least 33\ 1s, which is about 0.0005 per Alpha. You can multiply these by 6 to get the chance for any number, as it is very unlikely we doublecount by having at least 33 of two different numbers. So the chance of a "lucky number" happening by chance is about 0.0003 or one in 3300. Pretty unlikely, but rarer things happen all the time.


No comments:

Post a Comment

real analysis - How to find lim_{hrightarrow 0}frac{sin(ha)}{h}

How to find \lim_{h\rightarrow 0}\frac{\sin(ha)}{h} without lhopital rule? I know when I use lhopital I easy get $$ \lim_{h\rightarrow 0}...