# probability function?

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• Apr 13th 2010, 03:16 PM
shawli
probability function?
In a game of monopoly, a player cannot start until she throws a "double" with a set of two six-sided dice, i.e. both dice must show the same number (from 1 to 6) uppermost when tossed.

a) State the form of the probability distribution of $X$, the number of unsuccessful turns a player has before she manages to throw a "double".

--> This is the answer to the function but I'm confused about why: $X=(\frac{1}{6})(\frac{5}{6})^x$
Is the exponent $x$ only at the probability for unsuccessful rolls because there should never be more than one roll of success?

b) Find $P=(X>= 5)$

If X is for the number of unsuccessful turns made before a success, how do you calculate a "greater than or equal to" value if no total number of trials is given?

c) Find $P(X=5|X>=5)$
• Apr 13th 2010, 08:11 PM
mr fantastic
Quote:

Originally Posted by shawli
In a game of monopoly, a player cannot start until she throws a "double" with a set of two six-sided dice, i.e. both dice must show the same number (from 1 to 6) uppermost when tossed.

a) State the form of the probability distribution of $X$, the number of unsuccessful turns a player has before she manages to throw a "double".

--> This is the answer to the function but I'm confused about why: $X=(\frac{1}{6})(\frac{5}{6})^x$
Is the exponent $x$ only at the probability for unsuccessful rolls because there should never be more than one roll of success?

b) Find $P=(X>= 5)$

If X is for the number of unsuccessful turns made before a success, how do you calculate a "greater than or equal to" value if no total number of trials is given?

c) Find $P(X=5|X>=5)$

Geometric distribution - Google it.

(b) 1 - Pr(X < 5).

(c) Conditional probability. Use Bayes Theorem.