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Eight cavities in an injection-molding tool produce plastic connectors that fall into a common stream. A sample is chosen every several minutes. Assume that the samples are independent. a. What is the probability that five successive samples were all produced in cavity 1 of the mold? b. What is the probability that five successive samples were all produced in the same cavity of the mold? c. What is the probability that four out of five successive samples were produced in cavity 1 of the mold?

Short Answer

Expert verified
a. \( \frac{1}{32768} \); b. \( \frac{1}{4096} \); c. \( \frac{35}{32768} \).

Step by step solution

01

Identify Basic Probability

There are 8 cavities in the mold. Therefore, the probability that any one sample came from cavity 1 is \( \frac{1}{8} \). This is true for any of the cavities.
02

Probability for Part (a)

For part (a), we need five successive samples to come from cavity 1. The probability of each sample being from cavity 1 is \( \frac{1}{8} \). Thus, the probability of five successive samples coming from cavity 1 is \( \left(\frac{1}{8}\right)^5 = \frac{1}{32768} \).
03

Probability for Part (b)

For part (b), we need five successive samples to come from the same cavity. This could be any of the 8 cavities. First, calculate the probability for all samples coming from a particular cavity, which is \( \left(\frac{1}{8}\right)^5 \). Since there are 8 possible cavities, multiply the probability by 8: \( 8 \times \left(\frac{1}{8}\right)^5 = \frac{1}{4096} \).
04

Probability for Part (c)

For part (c), four out of five samples must be from cavity 1. There are 5 different patterns for one of the samples not being from cavity 1. The probability of four samples coming from cavity 1 is \( \left(\frac{1}{8}\right)^4 \) and for one sample not coming from cavity 1 would be \( \frac{7}{8} \). Thus, probability equals \( 5 \times \left(\frac{1}{8}\right)^4 \times \frac{7}{8} = \frac{35}{32768} \).

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Key Concepts

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

Injection Molding Processes
Injection molding is a popular and highly efficient manufacturing process used to produce a wide range of plastic products, including connectors, toys, and various component parts. The process involves melting plastic material and injecting it into a mold cavity, where it cools and solidifies into the desired shape. This technique allows for high precision and speed, making it suitable for mass production.

Each mold tool consists of multiple cavities that produce identical copies of a product simultaneously. For example, in an eight-cavity mold, eight plastic parts are produced with each manufacturing cycle. This setup is beneficial for increasing production rates and optimizing time efficiency. The output from each cavity falls into a common stream, making accurate tracking of individual cavity production challenging unless specified in the sampling or testing process.

The probability exercise mentioned highlights a scenario where we analyze samples from these cavities to understand the randomness of their occurrence. This is crucial for ensuring consistent quality and spotting potential defects or issues in specific cavities. Injection molding processes need strict controls and monitoring because any defect in a cavity can impact all products formed from it.
Independent Samples
In statistical analysis, independent samples refer to the selection method where the outcome of one sample does not influence or affect the outcome of another. For the given problem, each sample from the injection molding process is assumed to be independent. This means the cavity from which a particular sample is produced does not change the probability of another sample coming from the same or different cavity.

Understanding independent samples is vital for accurately evaluating probabilities in processes like injection molding.
  • Firstly, it helps in forming a precise model of the production process.
  • Secondly, it simplifies probability calculations by allowing the use of basic multiplication rules for independent events.

In our exercise, since the samples are assumed to be independent, each sample has an equal and unbiased chance of coming from any of the eight cavities. This uniformity across samples ensures easier computation and reliable probability assessments. However, in practice, independence might not always be present, and assumptions should be validated against real-world constraints.
Cavity Production Analysis
Cavity production analysis involves evaluating and understanding production data at the cavity level in a multi-cavity injection mold. This analysis is fundamental in monitoring the performance and quality output of each cavity.

Detection of any anomalies or defects originating from specific cavities can lead to targeted investigations and maintenance actions. By regularly analyzing cavity-specific production data, manufacturers can promptly address issues such as:
  • Cavity imbalances or blockages.
  • Fluctuations in product dimensions or quality.
  • Ejection or cooling time mismatches.

In the context of probability theory, cavity production analysis also delves into understanding the likelihood of successive samples emanating from the same cavity, as explored in the exercise. Identifying such trends is crucial to maintaining stringent quality standards and ensuring uniformity across all manufactured components.

Overall, employing cavity production analysis equips manufacturers with the insights needed to optimize production processes, reduce waste, and enhance product quality and consistency.

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Most popular questions from this chapter

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