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The paper referenced in Example 6.24 ("Estimating Waste Transfer Station Delays Using GPS," Waste Management [2008]: 1742-1750) describing processing times for garbage trucks also provided information on processing times at a second facility. At this second facility, the mean total processing time was 9.9 minutes and the standard deviation of the processing times was 6.2 minutes. Explain why a normal distribution with mean 9.9 and standard deviation 6.2 would not be an appropriate model for the probability distribution of the variable \(x=\) total processing time of a randomly selected truck entering this second facility.

Short Answer

Expert verified
A normal distribution with mean 9.9 and standard deviation 6.2 would not be appropriate for modeling the total processing time of a randomly selected truck entering the second facility because the normal distribution assumes no negative values. In this context, a negative processing time is not possible, and given the large standard deviation relative to the mean, the probability of negative processing times is significant. Therefore, using a normal distribution would not accurately represent the processing times in this situation.

Step by step solution

01

Understanding the Normal Distribution

A normal distribution is a continuous probability distribution that is symmetric about its mean (μ) and is characterized by its mean and standard deviation (σ). The bell-shaped curve has half of the data above the mean and half of the data below the mean. The probability of an event occurring within one, two, or three standard deviations from the mean are approximately 68%, 95%, and 99.7%, respectively. The normal distribution assumes that there are no negative values.
02

Considering the given data

In this analysis, we have the mean total processing time (9.9 minutes) and standard deviation (6.2 minutes) for garbage trucks at a second facility.
03

Analyzing the possibility of negative values

The first property we need to consider is the fact that normal distribution assumes no negative values. However, in this case, since the standard deviation is large (6.2 minutes) relative to the mean (9.9 minutes), it is possible for some processing times to be less than the mean by more than 9.9 minutes, resulting in negative processing times. A negative processing time makes no sense in this context, as a truck cannot have a negative time spent on processing.
04

Conclusion

Since a normal distribution assumes no negative values, and the given data has the possibility of negative processing times, it would not be an appropriate model for the probability distribution of the variable \(x=\) total processing time of a randomly selected truck entering this second facility.

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Key Concepts

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

Mean Total Processing Time
Mean total processing time is a statistical measure that represents the average time taken for a process to complete. In real-world scenarios, like the processing time for garbage trucks at a facility, it serves as an indicator of operational efficiency. However, the mean on its own can be misleading if not considered alongside the spread of the data, which is where standard deviation comes into play.

For instance, a facility with a mean processing time of 9.9 minutes suggests that on average, a truck will spend about 10 minutes at the facility. This average is a central point around which the actual processing times vary. It's crucial to remember that while the mean gives us a central tendency, it doesn't provide information about the individual variances from this central point. Therefore, knowing only the mean is insufficient to fully understand the processing time without the context provided by other statistics, such as standard deviation.
Standard Deviation
Standard deviation is a measure of the amount of variation or dispersion of a set of values. A low standard deviation indicates that the values tend to be close to the mean, whereas a high standard deviation indicates that the values are spread out over a wider range.

In the given exercise, the standard deviation is 6.2 minutes compared to the mean time of 9.9 minutes. This significant standard deviation relative to the mean indicates that the processing times are quite spread out. Some trucks may finish much faster than the average, while others may take much longer. When standard deviation is wide in relation to the mean, it suggests a large variability in processing times, which can challenge the assumption of a normal distribution that typically depicts less extreme variability.
Probability Distribution
A probability distribution is a mathematical function that provides the probabilities of occurrence of different possible outcomes in an experiment. It is a statistical tool that helps to describe the likelihood of various results from a random process.

In the context of the garbage facility, the probability distribution would allow us to determine the likelihood of a truck completing its processing in, say, between 5 to 10 minutes. It's essential in operational contexts, as it aids in predicting outcomes and making informed decisions based on the likelihood of different processing times. However, the type of probability distribution applied to a particular scenario must fit the characteristics of the data to provide accurate predictions.
Continuous Probability Distribution
Continuous probability distributions apply to scenarios where the variable can take on an infinite number of values within a given range. Unlike discrete distributions, which are used for countable outcomes, continuous distributions can model outcomes that are measurements, like time or distance.

The normal distribution is one such continuous probability distribution and is defined by its mean and standard deviation. It is characterized by its familiar bell curve, where most outcomes cluster around the mean. However, not all continuous data are suited to the normal distribution. The scenario in the exercise, with the potential for negative processing times due to the high standard deviation, violates one of the fundamental properties of a normal distribution: it does not accommodate negative values. Therefore, an alternative continuous probability distribution that can accommodate the actual range of processing times, including the impossibility of negative times, would be more appropriate for modeling the processing times of the trucks at the facility.

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Most popular questions from this chapter

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