Question 3 (14)
Suppose that you repeatedly play a game where you roll a fair six-sided die. You win $10 if the number of dots
faces up is 6. Otherwise, you win $1. Let $S_n$ be the total amount that you win after $n$ games and assume that
you don't have any money in the beginning.
(a) (2) Find $E[S_{10}]$
(b) (2) Find $VAR[S_{10}]$.
(c) (2) Find $COV(S_{10}, S_{20})$.
For the following questions (c) to (g), only give a clear mathematical expression and no need to provide a
numerical answer.
(d) (2) Find the probability that you win $28 in 10 games, $P[S_{10} = 28]$.
(e) (2) Find $P[S_{30} = 120|S_{10} = 28]$.
(f) (2) Find $P[S_{30} = 120 \cap S_{10} = 28]$.
(g) (2) Assume that you now start out with $10 and each time you play the game costs you $4. The cost of
playing the game is paid after completing 10 times. What is the probability that you have money larger than $5
after playing the game 10 times?