In a game, a man wins ₹ 8 for getting a number greater than 3 and loses ₹ 3 otherwise, when a fair die is thrown. The man decided to throw a die 4 times but to quit as and when he gets a number greater than 3. If X denotes the amount which the man wins or loses, then which of the following are correct?
(A) All the possible values of X are 8, 5, 2 and -1.
(B) The probability distribution of X is:
X 8 5 2 -1 -12 P(X) 1/2 1/4 1/8 1/16 1/16
(C) The mean value of X is 75/16.
(D) The variance of X is 6615/256.
Choose the correct answer from the options given below:
In a game, a man wins ₹ 8 for getting a number greater than 3 and loses ₹ 3 otherwise, when a fair die is thrown. The man decided to throw a die 4 times but to quit as and when he gets a number greater than 3. If X denotes the amount which the man wins or loses, then which of the following are correct?
(A) All the possible values of X are 8, 5, 2 and -1.
(B) The probability distribution of X is:
| X | 8 | 5 | 2 | -1 | -12 |
|---|---|---|---|---|---|
| P(X) | 1/2 | 1/4 | 1/8 | 1/16 | 1/16 |
(C) The mean value of X is 75/16.
(D) The variance of X is 6615/256.
Choose the correct answer from the options given below:
Solution
The probability of getting a number greater than 3 (i.e., 4, 5, or 6) is .
The probability of getting a number less than or equal to 3 (i.e., 1, 2, or 3) is .
Case 1: First throw shows a number > 3
The man wins ₹8 and quits.
Case 2: First throw ≤ 3, second throw > 3
The man loses ₹3, then wins ₹8 and quits.
Case 3: First two throws ≤ 3, third throw > 3
The man loses ₹3 twice, then wins ₹8 and quits.
Case 4: First three throws ≤ 3, fourth throw > 3
The man loses ₹3 thrice, then wins ₹8 and quits.
Case 5: All four throws ≤ 3
The man loses ₹3 four times and must quit after 4 throws.
The possible values of X are: 8, 5, 2, -1, and -12.
Statement (A) is incorrect as it does not include -12.
The probability distribution matches statement (B):
| X | 8 | 5 | 2 | -1 | -12 |
|---|---|---|---|---|---|
| P(X) | 1/2 | 1/4 | 1/8 | 1/16 | 1/16 |
Statement (B) is correct.
The mean value of X:
Statement (C) is correct.
For variance, calculate :
The variance:
Statement (D) is correct.
Therefore, statements (B), (C), and (D) are correct.
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