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Exercise \(7.9\) introduced the following probability distribution for \(y=\) the number of broken eggs in a carton: $$ \begin{array}{cccccc} y & 0 & 1 & 2 & 3 & 4 \\ p(y) & .65 & .20 & .10 & .04 & .01 \end{array} $$ a. Calculate and interpret \(\mu_{y} .\) b. In the long run, for what percentage of cartons is the number of broken eggs less than \(\mu_{y}^{?}\) Does this surprise you? c. Why doesn't \(\mu_{y}=(0+1+2+3+4) / 5=2.0\). Explain.

Short Answer

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a) The mean (饾渿饾懄) is 0.50 which is the average number of broken eggs in a carton. b) 85% of the cartons have less than the average number of broken eggs, which is not surprising as the probabilities are skewed towards 0 and 1 broken eggs. c) The arithmetic mean is not the same as 饾渿饾懄 because the mean in a probability distribution takes into account the probability of each outcome, not just the uniform dispersion of values.

Step by step solution

01

Calculate the expectation (饾渿饾懄)

The expectation or mean of a random variable Y, denoted as 饾渿饾懄, is calculated by multiplying each possible outcome by their respective probability and summing these products. Using the given probabilities, we compute it as follows: 饾渿饾懄 = (0 脳 0.65) + (1 脳 0.20) + (2 脳 0.10) + (3 脳 0.04) + (4 脳 0.01) = 0.50. This is interpreted as the average number of broken eggs in a carton.
02

Find the percentage of cartons with less than the average number of broken eggs

From the distribution, we can see that 0 and 1 are the only outcomes that are less than the average 饾渿饾懄 = 0.50, with the probabilities of these outcomes being 0.65 and 0.20 respectively. The sum of these probabilities will give the percentage of cartons with less than the average number of broken eggs. Hence, the required percentage = 0.65 + 0.20 = 0.85 or 85%.
03

Explain why the arithmetic mean is not the same as \(\mu_{y}\)

The arithmetic mean is not the same as the expected value because they both are computed differently. The arithmetic mean takes into consideration the uniform distribution of all values of random variable Y (sum of all values divide by total), while the expected value (mean) uses the probability of each outcome. Because the distribution here is not uniform (as can be seen from the different probabilities for each outcome), it results in a different value than the arithmetic mean.

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Key Concepts

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

Expected Value
Expected value is a concept used to describe the average outcome of a random process if it were repeated many times. In our example, this translates to the number of broken eggs in a carton observed on average in the long run. To calculate it, we multiply each potential outcome by its respective probability, then sum these products. Here鈥檚 how it works for the given problem:
  • Outcome 0: 0 broken eggs with a probability of 0.65, contributes to the expected value as \(0 \times 0.65 = 0\).
  • Outcome 1: 1 broken egg with a probability of 0.20, contributes \(1 \times 0.20 = 0.20\).
  • Outcome 2: 2 broken eggs with a probability of 0.10, contributes \(2 \times 0.10 = 0.20\).
  • Outcome 3: 3 broken eggs with a probability of 0.04, contributes \(3 \times 0.04 = 0.12\).
  • Outcome 4: 4 broken eggs with a probability of 0.01, contributes \(4 \times 0.01 = 0.04\).
Adding these contributions gives us an expected value \(\mu_{y} = 0 + 0.20 + 0.20 + 0.12 + 0.04 = 0.50\). This means that, on average, there will be 0.5 broken eggs per carton.
Random Variable
A random variable is essentially a way to map outcomes of a random process to numerical values. In our example, the random variable \(Y\) represents the number of broken eggs in a carton. Each possible outcome (0, 1, 2, 3, and 4 broken eggs) is associated with a probability, indicating how likely each outcome is to occur.Understanding random variables is crucial in statistics, as they help translate real-world phenomena into mathematical language that can be analyzed statistically. The probable occurrence of different outcomes is captured by the probability distribution, which in this case, we have as:
  • \(Y = 0\) with \(p(y) = 0.65\)
  • \(Y = 1\) with \(p(y) = 0.20\)
  • \(Y = 2\) with \(p(y) = 0.10\)
  • \(Y = 3\) with \(p(y) = 0.04\)
  • \(Y = 4\) with \(p(y) = 0.01\)
These probabilities reflect the likelihood of encountering a specific number of broken eggs in a carton.
Arithmetic Mean
The arithmetic mean is a basic concept in statistics used to find the central value of a set of numbers. It is calculated by adding up all the numbers and dividing by the total count of numbers. In the case of our broken eggs example, one might mistakenly think the arithmetic mean of the numbers 0, 1, 2, 3, and 4 is 2.0, dividing their sum 10 by 5. However, the arithmetic mean does not take the probabilities of each outcome into account. The key distinction is that the arithmetic mean assumes that each number has equal likelihood, which often isn鈥檛 the case in real-world data. Here, because the distribution of broken eggs isn鈥檛 uniform (each number does not have the same likelihood of appearing), the expected value \(\mu_{y}\) computed considering the probability of each outcome gives a more accurate central tendency metric in this scenario. That's why the expected value differed at 0.50, not 2.0.

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