Q. 2 A charity prints scratch cards each of which contain 3 squares. Each square may contain a star or an X and the printing process independently decides which symbol will be on each square such that the probability of a star is 20%. When someone buys a card they scratch the three boxes to reveal a star or an X in each box. The amount that is paid out to the player depends on the total number of stars uncovered on the card as follows Number of stars | 0 | 1 | 2 | 3 Prize Amount | $0 | $2 | $5 | $20 a) Let X be the amount paid out for a random ticket. Find the probability mass function of X. b) If it costs 5 cents to print each ticket and tickets sell for $2, what is the expected amount of profit that the charity will make on each ticket? c) What is the expected number of tickets I need to buy if I keep buying tickets until one of the tickets wins $20?
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The probability of getting a star in a single square is $p = 0.2$, and the probability of getting an X is $1 - p = 0.8$. Since there are 3 squares, the number of stars follows a binomial distribution with parameters $n = 3$ and $p = 0.2$. The probability mass Show more…
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