In: Math
Consider the following game: Three cards are labeled $1, $4, and $7. A player pays a $9 entry fee, selects 2 cards at random without replacement, and then receives the sum of the winnings indicated on the 2 cards.
a) Calculate the expected value and standard deviation of the random variable "net winnings" (that is, winnings minus a $9 entry fee)
b) Suppose a 4th card, labelled k, is added to the game but the player still selects two cards without replacement. What is the value of k which makes the game fair (i.e makes expected net winnings = $0)
Please rate. Cheers !!!
a).
P (X1) | 1/3 |
P (X2) | 1/2 |
X1 | X2 | Y (X1 + X2) |
1 | 4 | 5 |
1 | 7 | 8 |
4 | 1 | 5 |
7 | 1 | 8 |
4 | 7 | 11 |
7 | 4 | 11 |
therefore P (Y) = P (X1) * P (X2)
Y | Freq. | P (Y) | W (Y - 9) | P (W) | W * P (W) | W ^2 | W ^2 * P (W) |
5 | 2 | 1/3 | -4 | 1/3 | -1 1/3 | 16 | 5 1/3 |
8 | 2 | 1/3 | -1 | 1/3 | - 1/3 | 1 | 1/3 |
11 | 2 | 1/3 | 2 | 1/3 | 2/3 | 4 | 1 1/3 |
sum | 1 | 1 | -1 | 7 |
b ).
X1' | X2' | Y' (X1' +X2') |
1 | 4 | 5 |
1 | 7 | 8 |
1 | K | K + 1 |
4 | K | K + 4 |
4 | 1 | 5 |
4 | 7 | 11 |
7 | 4 | 11 |
7 | K | K + 7 |
7 | 1 | 8 |
K | 1 | K + 1 |
K | 7 | K + 7 |
K | 4 | K + 4 |
72 + 6K | ||
P (X1') | 1/4 | |
P (X2') | 1/3 |
Y' | Freq. | P (Y') | W (Y'- 9) |
11 | 2 | 1/6 | 2 |
5 | 2 | 1/6 | -4 |
8 | 2 | 1/6 | -1 |
K + 1 | 2 | 1/6 | K - 8 |
K + 4 | 2 | 1/6 | K - 5 |
K + 7 | 2 | 1/6 | K - 2 |
Sum | 12 | 1 | |