# Statistics

• Feb 26th 2008, 01:10 PM
Chez_
Statistics
I need help with this question please.
The random variable X is given by the sum of the scores when two ordinary dice are thrown.
i) i need to use the shape of the distribution to find E(X)=U
( but i dont know what i need to draw for that...)
From this i should also be able to valculate Var(X)=0^2

Finally i need to find P(X<U) and P(X>U+o) < could someone please tell what these mean and how to calculate .

Thank you
• Feb 27th 2008, 03:37 AM
CaptainBlack
Quote:

Originally Posted by Chez_
I need help with this question please.
The random variable X is given by the sum of the scores when two ordinary dice are thrown.
i) i need to use the shape of the distribution to find E(X)=U
( but i dont know what i need to draw for that...)
From this i should also be able to valculate Var(X)=0^2

Finally i need to find P(X<U) and P(X>U+o) < could someone please tell what these mean and how to calculate .

Thank you

You need to calculate the probability of the outcomes X=2, 3, ..., 12 by
counting how many of the 36 possible outcomes (when the dice are
distinguishable) give each score and then dividing by 36:

P(X=2)=1/36
P(X=3)=2/36
P(X=4)=3/26
P(X=5)=4/36
:
:
P(X=12)=1/36

Once you have these probabilities your notes will tell you how to compute the
expectation and varianve etc.

RonL