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A box contains ten sealed envelopes numbered \(1, \ldots, 10\). The first five contain no money, the next three each contains \(\$ 5\), and there is a \(\$ 10\) bill in each of the last two. A sample of size 3 is selected with replacement (so we have a random sample), and you get the largest amount in any of the envelopes selected. If \(X_{1}, X_{2}\), and \(X_{3}\) denote the amounts in the selected envelopes, the statistic of interest is \(M=\) the maximum of \(X_{1}, X_{2}\), and \(X_{3}\). a. Obtain the probability distribution of this statistic. b. Describe how you would carry out a simulation experiment to compare the distributions of \(M\) for various sample sizes. How would you guess the distribution would change as \(n\) increases?

Short Answer

Expert verified
Distribution: \( P(M=0)=\frac{1}{8}, P(M=5)=\frac{27}{125}, P(M=10)=1-P(M=0)-P(M=5) \). For simulations, sample enlarges and shows increasing chance of higher values.

Step by step solution

01

Identify possible values of M

Since the envelopes can contain \(0, \)5, or $10, the maximum value \( M \) of \( X_1, X_2, \) and \( X_3 \) can only take one of these three values. Thus, possible values for \( M \) are 0, 5, and 10.
02

Calculate probability of M = 0

\( M = 0 \) happens only if all three envelopes contain \(0. With replacement, the probability of selecting a \)0 is \( \frac{5}{10} = \frac{1}{2} \). Thus, \( P(M = 0) = \left( \frac{1}{2} \right)^3 = \frac{1}{8} \).
03

Calculate probability of M = 5

\( M = 5 \) happens if at least one envelope contains \(5, but none contain \)10. Probability of selecting a \(5 and then not selecting \)0 or $10 is \( \left( \frac{3}{10} \right) \left( \frac{1}{5} \right)^2 + \left( \frac{1}{2} \right)^2 \left( \frac{3}{10} \right) = \frac{27}{125} - \frac{1}{8} \).
04

Calculate probability of M = 10

\( M = 10 \) requires at least one envelope with \(10. Probability of selecting a \)10 at least once is \( 1 - P(M = 0 \text{ or } M = 5) \). Combine probabilities from Steps 2 and 3.
05

Conduct simulation experiments

Construct random envelopes with values 0, 5, or 10 and sample with increasing \(n\). Count instances of maximum values in repeated simulations and compare results.
06

Guess the distribution changes with increasing n

As \( n \) increases, \( M \) becomes concentrated around the maximum envelope value due to increasing chances of selecting higher amounts at least once. Predict an eventual Gaussian distribution.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Random Sampling
Random sampling is an essential concept in probability and statistics. It involves selecting a sample from a larger population in such a way that each member of the population has an equal chance of being chosen. In the original exercise, we have a box containing ten envelopes, each with predefined values. When we say a 'sample of size 3 is selected with replacement', it means for each pick, you return the envelope back into the box before picking again. This ensures each envelope still has the same probability of being picked in each draw.

This method of sampling with replacement is crucial to maintaining the randomness of the selection. By doing so, you ensure that the probability of picking an envelope with $0, $5, or $10 remains constant across trials. This setup forms the basis for analyzing and understanding statistical distributions, as it emulates conditions where samples are taken independently from the population.
Simulation Experiment
A simulation experiment is a powerful tool in probability to understand and predict complex distributions. It's particularly useful when analytical solutions are complicated or when trying to observe behavior over many trials. In the context of our exercise, a simulation would involve repeatedly drawing samples from the box of envelopes and recording the maximum value found in each set of three picks.

Here's a simplified step-by-step guide on how to conduct this simulation:
  • Create a digital model of the box with the 10 envelopes.
  • Select an envelope, record the amount, replace it back, and repeat till you have three amounts.
  • Determine the maximum for that set of three and record it.
  • Repeat the above steps for a significant number of trials to approximate the distribution of the maximum value.
This simulated environment provides tangible insights into how often the maximum amount occurs and helps predict how the distribution might behave as sample size becomes larger.
Probability Calculation
Calculating probabilities in this exercise means understanding the likelihood of different outcomes for the maximum value statistic. This involves acknowledging the different possible situations in which each maximum amount can occur.

1. **Probability of Maximum Being 0**: This happens if all three selected envelopes are 0. The calculation uses \( P(M=0) = \left( \frac{1}{2} \right)^3 = \frac{1}{8} \) given half of the envelopes are 0.
2. **Probability of Maximum Being 5**: Here, at least one envelope is 5, and none is 10. Use combinatorial analysis to determine this by excluding 10 from the possibilities.
3. **Probability of Maximum Being 10**: This is calculated as what's left after accounting for all non-10 selections: \( P(M=10) = 1 - (P(M=0) + P(M=5)) \).

These probabilities give insight into understanding how likely you are to draw maximum amounts of 0, 5, or 10 when randomly sampling.
Maximum Value Statistic
The maximum value statistic represents the highest value observed from a set of random samples. In this exercise, the statistic of interest is the largest amount found in the three selected envelopes. This measurement is crucial because it gives a sense of the upper bound of outcomes for the given trials.

The interesting aspect of the maximum value statistic is how its distribution changes with different sample sizes. When you increase the number of samples (the number of times envelopes are drawn), you're more likely to observe higher values at least once, simply because you have more opportunities to draw higher amounts. This behavior is why, as you increase the sample size in the simulation, the distribution shifts, possibly moving towards a Gaussian shape.

Understanding the maximum value helps in decision-making where peak performance or extreme results are significant, like in financial risk assessment or quality control scenarios.

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