Probability Distributions Quiz
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Questions and Answers

What is the mean of a hyper-geometric variable represented as?

  • $E(X) = np$ (correct)
  • $E(X) = N/n$
  • $E(X) = pq$
  • $E(X) = n(N - n)$
  • The variance of a hyper-geometric variable can be calculated using the formula $Var(X) = npq \cdot \frac{N - n}{N - 1}$.

    True (A)

    In a lot containing 30 items, 6 are defective. What is the probability of selecting a random sample of five items containing no defective items?

    0.4783

    The expected value of the number of red chips drawn when taking two chips out of a bowl containing six red and four blue chips is ______.

    <p>1.2</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Mean = The average of a probability distribution Variance = A measure of the dispersion of a probability distribution Hyper-geometric Distribution = Models scenarios without replacement Geometric Distribution = Models scenarios with independent trials</p> Signup and view all the answers

    What type of random variable is used to calculate the probability of getting the first success on a specific trial?

    <p>Geometric random variable (B)</p> Signup and view all the answers

    The hypergeometric distribution deals with sampling with replacement.

    <p>False (B)</p> Signup and view all the answers

    What is the probability that the 10th person you encounter in a town with 4% teachers is a teacher?

    <p>0.0031</p> Signup and view all the answers

    The mean of a geometric distribution with probability of success $p$ is _____

    <p>1/p</p> Signup and view all the answers

    Match the terms with their definitions:

    <p>Geometric Distribution = The probability of the first success on trial k Hypergeometric Distribution = Sampling without replacement from a finite population Mean = The average of a probability distribution Variance = A measure of the dispersion of a probability distribution</p> Signup and view all the answers

    If 2% of tires produced by a company are defective, what is the probability that the first defect is found in the first 5 samples?

    <p>0.9171 (B)</p> Signup and view all the answers

    The variance of a geometric distribution with probability $p$ is calculated as $p/(1-p)^2$.

    <p>False (B)</p> Signup and view all the answers

    What would you expect the number of tires to test until the first defective one is found if 2% of tires are defective?

    <p>50</p> Signup and view all the answers

    What does a geometric random variable represent in probability theory?

    <p>The number of trials until the first success (D)</p> Signup and view all the answers

    The probability of needing x trials for the first success in a geometric distribution decreases as x increases.

    <p>False (B)</p> Signup and view all the answers

    Define a geometric random variable.

    <p>A geometric random variable is the number of trials required to get the first success in a Bernoulli process.</p> Signup and view all the answers

    In a geometric distribution, the probability of success on each trial is denoted by ______.

    <p>p</p> Signup and view all the answers

    If a fair coin is tossed until a head appears, what is the probability that exactly three tosses are needed?

    <p>1/8 (D)</p> Signup and view all the answers

    In the scenario of rolling a die until a six appears, the probability of needing at least 3 rolls is higher than needing at most 4 rolls.

    <p>True (A)</p> Signup and view all the answers

    What is the formula to calculate the probability that at most x trials are needed for the first success in a geometric distribution?

    <p>P(X ≤ x) = P(X = 1) + P(X = 2) + ... + P(X = x)</p> Signup and view all the answers

    Match the following scenarios with their corresponding probabilities:

    <p>Tossing a coin, getting a head on the first toss = P = p First success occurs on the third trial after two failures = P = (1-p)²p At least one head in three tosses = 1 - P(X = 0) Rolling a die and getting a six = P = p</p> Signup and view all the answers

    Flashcards

    Geometric Probability

    The probability of getting the first success on the xth trial in a sequence of independent Bernoulli trials.

    Geometric Random Variable

    A discrete random variable representing the number of trials needed to get the first success in a sequence of independent Bernoulli trials.

    Mean of Geometric Distribution

    The average number of trials needed to achieve the first success in a sequence of independent Bernoulli trials; calculated as 1/p where p is the probability of success.

    Variance of Geometric Distribution

    The average squared deviation of the number of trials from the mean, calculated as (1-p)/p^2 where p is the probability of success.

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    Hypergeometric Distribution

    A probability distribution that describes probabilities of success in drawing a sample in a population without replacement.

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    Binomial Distribution

    A probability distribution that describes the number of successes in a fixed number of independent Bernoulli trials.

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    Sampling with replacement

    Each drawn item is put back into the pool of potential items before the next draw. This process ensures that the probability of drawing any particular item remains unchanged in each draw.

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    Sampling without replacement

    Each drawn item is not returned to the pool of potential items. This changes the probability of selecting subsequent items.

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    Hypergeometric Probability

    The probability of getting a specific number of successes (e.g., men, defective items) in a sample without replacement from a finite population.

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    Mean of Hypergeometric Variable (E(X))

    The expected value of a hypergeometric variable. It's calculated as n * (N1/N); where 'n' is the sample size, 'N1' is the number of successes in the whole population, and 'N' is the total population size.

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    Variance of Hypergeometric Variable (Var(X))

    The spread of the hypergeometric variable. It's calculated as [(n * (N1/N)) * ((N - n) / (N -1)) * ((N - N1) / N)], where 'n' is sample size, 'N1' is number of successes, 'N' is the whole population size.

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    Selection without Replacement

    Choosing items from a group, where once chosen, the item is not returned to the group.

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    Sample Size (n)

    The number of items that are chosen.

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    Geometric Distribution Formula

    The probability mass function of a geometric random variable X is P(X=x) = (1-p)^(x-1)*p, where p is the probability of success on a single trial and x is the number of trials needed to get the first success.

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    Geometric Distribution Example

    A fair coin is tossed until a head appears. The probability of getting a head on the first trial is 1/2. The probability of getting a head on the second trial is (1/2)(1/2) = 1/4. The probability of getting a head on the third trial is (1/2)(1/2)(1/2) = 1/8. The probability function in this case is P(X = x) = (1/2)^(x-1)(1/2) = (1/2)^x.

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    What does 'at most' mean in terms of geometric probabilities?

    'At most' means including the specific number of trials and all the trials before it. So, the probability of getting the first success in at most 3 trials would be the probability of getting the first success on the 1st, 2nd, or 3rd trial.

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    What does 'at least' mean in terms of geometric probabilities?

    'At least' means including the specific number of trials and all the trials after it. So, the probability of getting the first success in at least 3 trials would be the probability of getting the first success on the 3rd trial, on the 4th trial, on the 5th trial and so on.

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    Study Notes

    Probability Distributions

    • Geometric Random Variable: A Bernoulli trial is repeated until a success occurs. X represents the number of trials before the first success. The probability of x trials before the first success is given by (1-p)^(x-1) * p, where p is the probability of success on a single trial.

    • Probability Density Function (PDF) for Geometric Random Variable: A discrete random variable, X, is geometric if its PDF is:

    • P(X = x) = (1-p)^(x-1) * p, for x = 1, 2, ...

    • 0, otherwise

    • Mean and Variance of Geometric Distribution:

    • Mean (Expected Value): E(X) = 1/p

    • Variance: Var(X) = (1-p)/p²

    Hypergeometric Distribution

    • Key Difference: Sampling without replacement from a finite population. This is in contrast to the binomial distribution, which deals with sampling with replacement.

    • Probability Density Function (PDF) for Hypergeometric Distribution:

    • f(x) = [ (N₁ choose x) * (N - N₁ choose n - x) ] / (N choose n), for x, n—x >= 0 Where:

    • N = Total population size

    • N₁ = Number of items possessing a particular characteristic

    • n = Sample size

    • Constraints: N ≥ N₁, N ≥ n, and n − x ≤ N − N₁ are crucial for the formula to apply.

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    Description

    Test your knowledge on probability distributions, including geometric and hypergeometric distributions. This quiz will cover key concepts such as probability density functions, means, variances, and the differences between sampling with and without replacement.

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