Math question: probability
 

I need a little help here, my head isnt working today.

A chance of rolling any number on a die is 1/6.

Lets say I want to roll a “2”.

If I roll once there is a 1/6 chance of rolling a “2”.

How do I calculate the odds of rolling a “2” if I roll the dice ten times?

rolling a two consecutively 10 times would be

1 x 1 x 1 x 1 x 1 x 1 x 1 x 1 x 1 x 1
---------------------------------
6 x 6 x 6 x 6 x 6 x 6 x 6 x 6 x 6 x 6 = 1/a really big number

however, I don't know about just rolling ot once

Mantus: Do you mean what are the chances of rolling at least one 2 or rolling exactly one 2? I presume the former.

The easist way to do this is to think "what are the chances of me rolling NO 2s?"

On a single roll, the probability of not rolling a 2 is 5/6.
Hence the probability of not rolling a 2 ten times in a row is (5/6)¹⁰.

So the probability of NOT not rolling a 2 is one minus this:
1 - (5/6)¹⁰

Because rolling the die is independent between trials, Cowman's got it right:

P(getting "2" on each roll after n rolls) = 1/6^n.

However, it's been a long time since I've done this stuff!

That is the probability for rolling all 2s on ten rolls. I don't think that is what Mantus is looking for.

i THINK cowman's right. not sure, im not too hot in math.

see CSFilm's post. He's got it right. (Depending on what you mean by rolling a two)

yea the prize goes to csfilm

--edit--

misread posts :P

Sorry guys, that was proorly phrased.

I am looking the posibility of rolling at least one "2" out of 10 rolls.

For every 10 rolls you should roll 2, 1.67 times... if you are asking what the probability of rolling at least one 2 when you roll 10 times, it is basically 100% if not more than 100%...

It's impossible to have more than 100% probability.

If you're asking what is the probability of rolling at least one 2 in 10 rolls, one of the above posters had it right:

Take the total probability (1) and subtract the probability of rolling NO 2s. The math works out to be about an 83.8% probability of rolling at least one two, not quit as high as you had anticipated.

I am just quoting this because it is correct, and if you work it out you get 83% just like the last poster mentioned

Ah it just clicked in...I am very rusty with math. Perhaps it's time for me to take a class to refresh my memory, thanks guys :thumbsup: