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Imagine you roll a fair die ten times. Let X be a random variable denoting the number of times the resulting face is odd. What is the probability that X=1 ?

O 1/2​
O 10(1/2​)¹⁰
O (1/2​)⁹
O 9(1/2​)⁹
O (1/2​)¹⁰

1 Answer

6 votes

Final answer:

The probability of rolling exactly one odd number with a fair die in ten rolls is represented by the binomial probability formula, resulting in 10(1/2)^10 (option 2) or approximately 0.00977.

Step-by-step explanation:

The student is interested in the probability of obtaining exactly one odd number when a fair six-sided die is rolled ten times.


In probabilistic terms, the random variable X describes the number of times the resulting face is odd. To find the probability of X=1, we recognize that each die roll is an independent event, with the probability of getting an odd number (1, 3, or 5) being 1/2, since there are three odd faces out of six. Applying the concept of binomial probability, we use the binomial formula:

P(X=k) = C(n, k) × (p)^k × (q)^(n-k)

Where P(X=k) is the probability of k successes in n trials, C(n, k) is the binomial coefficient representing the number of combinations of n items taken k at a time, p is the probability of success on a single trial, and q is the probability of failure on a single trial.

For this situation, n = 10 (number of rolls), k = 1 (one odd number), p = 1/2 (success probability), and q = 1/2 (failure probability). Plugging these into the formula gives:

P(X=1) = C(10, 1) × (1/2)^1 × (1/2)^(10-1)

Calculating this, we get:

P(X=1) = 10 × (1/2)^1 × (1/2)^9

P(X=1) = 10 × (1/2)^10

P(X=1) = 10/1024, or approximately 0.00977

So, the correct answer is 10(1/2)¹⁰, which represents the probability of obtaining exactly one odd number when the die is rolled ten times.

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