# Probability of throwing a 6 in dice

1. Jan 25, 2010

### Dell

i throw a dice until i get a result (6) 20 times, what is the probability that i will throw the dice more than 100 times?

i made X=amount of times i throw the dice

so now im looking for P(X>100)

i think that i can say X~B(n, 1/6)
but the problem is that i dont know n, since it is anything over 100

2. Jan 26, 2010

### TaylorRatliff

3. Jan 26, 2010

### jambaugh

http://en.wikipedia.org/wiki/Geometric_distribution" [Broken]

Last edited by a moderator: May 4, 2017
4. Jan 26, 2010

### Count Iblis

In this problem you can always throw the dice 100 times. If you get 20 or more sixes, you needed to throw the dice 100 times or less to get exactly 20 sixes. If you haven't reached 20 yet, then that means that you would have reached 20 had you thrown the dice more than 100 times.

So, the desired probability is the probability that after 100 dice throws you have less than 20sixes.

5. Jan 27, 2010

### Dell

thanks, thats great