Maths help - statistics - dice rolling

[Alan]

Assume we have two normal 6 sided dice from a typical monopoly set.

What are the chances of rolling a double ?

I believed it was 1 in 36 (well actually 1 in 35) but then it got me thinking you are rolling two dice so assume the first one lands on "2" the chances for a subsequent dice roll to land on "2" is 1 in 6.

Therefore if you don't care what double you get the chances are 1 in 6 ?

 

[kirennia]

First of all, see how many total possibilities there are = 36
Then see how many different kind of doubles you can get = 6

6/36 is the possibility of rolling A double. If you only want one kind of double then of course it's 1/36. 2 doubles it's 2/36 etc etc.

 

[kiliarien]

Yeah one particular double would be 1/36. Any double at all would be 1/6.

 

[Cozak]

Yeah one particular double would be 1/36. Any double at all would be 1/6.

Any double at all cant be 1/6 as you need to roll more than 6 times (1 dice) to roll a double? I know you can roll a double with one dice and multiple rolls, obviously, but Im not so sure this is what the question is asking? Maybe Iam seeing this wrong, but it seems wierd.

 

[psyco]

yes, but why?

also, if the dices are different sizes you couldn't equate it, unless you are maths genius... that is if you roll em at the same time... let me explain... place 2 dice next to each other in your hand, with the same number on top, then roll them both at the same time you will likely get the same number, unless they bash into things... if they are different sizes they probably wont hit the same number... but that's not really probability, more phisics

 

[chretien]

Any double at all cant be 1/6 as you need to roll more than 6 times (1 dice) to roll a double? I know you can roll a double with one dice and multiple rolls, obviously, but Im not so sure this is what the question is asking? Maybe Iam seeing this wrong, but it seems wierd.

He's rolling two dice:

Assume we have two normal 6 sided dice from a typical monopoly set.

There are (as Kirennia pointed out) 36 different results you can get from all combinations of 2 dice. Each combination is as likely as any other. 6 of those combinations are doubles (1-1, 2-2, 3-3, 4-4, 5-5 and 6-6). So 6/36 or 1/6 rolls are doubles.
You can see it easily if you draw a table showing all the results.

      1      2    3      4     5     6 <-- Dice 1
1    *      3     4      5     6     7
2    3      *     5      6     7     8
3    4      5     *      7     8     9
4    5      6     7      *     9     10
5    6      7     8      9     *    11
6    7      8     9      10    11   *
^
Dice 2

In the table above I've replaced all the double results with asterisks (*) to make it easier to see.

 

[Thorwyn]

Well... you can also use the "logical" way.

Take one dice. Now say a number between 1 and 6 and roll the dice. Obviously, there´s a 1/6 chance, that you´re rolling the number you have predicted.
Now just replace "yourself" with the second dice and let it predict the number.... tada!

 

[Jeremiah]

if the dices are different sizes you couldn't equate it, unless you are maths genius... that is if you roll em at the same time... let me explain... place 2 dice next to each other in your hand, with the same number on top, then roll them both at the same time you will likely get the same number, unless they bash into things... if they are different sizes they probably wont hit the same number... but that's not really probability, more phisics

The odds on 1/6 of rolling a double are on the assumption that every number has the exact same chance of appearing. The starting state of the dice isnt taken into consideration as we are assuming it has no bearing on influencing what number appears. Even if the dice were of different sizes, we would assume that each dice number has an equal chance of appearing - this is based on the assumption that when you "roll" the dice, you are giving it a proper roll and not just dropping it on the table

 

[Huntingtons]

with 2 dices, whats the chance of getting a pair (a determined pair, lets say 6) in 7 rolls? just worked with it in math today, or our teaches asked us that question >_<

 

[Lamp]

There are 6 ways of rolling doubles out of 36 ways of rolling two dice.

For an n-sided dice, the probability = n x (1/n^2) = 1/n of rolling doubles with it.

 

[Neffneff]

with 2 dices, whats the chance of getting a pair (a determined pair, lets say 6) in 7 rolls? just worked with it in math today, or our teaches asked us that question >_<

i hope i dont sound naive or anything, but isnt it just a 7 in 36 chance?

i.e. 7 chances of landing a 1 in 36 chance?

EDIT: although now i post this, it makes me wonder what i'd say if you asked what the chance was of getting two sixes if you rolled the dice say...100 times.

 

[crispy]

with 2 dices, whats the chance of getting a pair (a determined pair, lets say 6) in 7 rolls? just worked with it in math today, or our teaches asked us that question >_<

the chance of getting 6'ers as a pair is 1/36... chance of NOT getting that pair is therefore 35/36.. the chance of NOT getting that roll in 7 rolls is (35/36)^7 = something. Then you can calc the chance of GETTING the roll, since theres always a chance to roll something ^_^ bad explanation but whatever

edit:
chance should be 17.89%

 

[Pirkel]

Been rolling dice the last 6 hours I'll see dice in my nightmares tonight.

 

[Lamp]

Been rolling dice the last 6 hours

Why ? lol

 

[Miril]

the chance of getting 6'ers as a pair is 1/36... chance of NOT getting that pair is therefore 35/36.. the chance of NOT getting that roll in 7 rolls is (35/36)^7 = something. Then you can calc the chance of GETTING the roll, since theres always a chance to roll something ^_^ bad explanation but whatever

edit:
chance should be 17.89%

He's right, the chance of getting a (I assume at least one) pre-determined pair in 7 rolls = 1 - the chance of getting none of those pairs in those 7 rolls = 1 - (35/36)^7 = indeed 0,1789

 

[Lamp]

There are loads and loads of articles dealing with probability and dice rolls on the internet. Just type in dice+probabilities+pdf to google

 

[Boni]

Sod google, just play backgammon lots

 

[Lamp]

I used to know a guy down my local pub who was an ace at backgammon. He taught me how to play, and ofc he beat me everytime, but I could never really get into it. The game still mystifies me somewhat.