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4-10. The probability density function of the length of a cutting blade is \(f(x)=1.25\) for \(74.675.2)\) (c) If the specifications for this process are from 74.7 to 75.3 millimeters, what proportion of blades meets specifications?

Short Answer

Expert verified
(a) 0.25 (b) 0.5 (c) 0.75

Step by step solution

01

Understand the Problem

We are dealing with a uniform probability density function (pdf) where the density function is constant, specifically \(f(x) = 1.25\) for the interval \(74.6 < x < 75.4\) millimeters. We need to find probabilities related to this pdf.
02

Determine Total Range

The total length of the interval \(74.6 < x < 75.4\) is calculated as: \(75.4 - 74.6 = 0.8\). The probability density dictates that this entire interval will have a probability of 1, since it's a uniform distribution.
03

Solve Part (a)

For \(P(X < 74.8)\), we calculate the length of the interval \(74.6 < x < 74.8\), which is \(74.8 - 74.6 = 0.2\). The probability for the subinterval is \(0.2 \times 1.25 = 0.25\).
04

Solve Part (b)

For \(P(X < 74.8\) or \(X > 75.2)\), find probability in two intervals: \(74.6 < x < 74.8\) and \(75.2 < x < 75.4\). Each interval has length \(0.2\), and total probability \(0.2 \times 1.25 = 0.25\) for each. So, \(0.25 + 0.25 = 0.5\).
05

Solve Part (c)

The specification interval is \(74.7 < x < 75.3\), spanning \(75.3 - 74.7 = 0.6\). The probability of a blade meeting this specification is \(0.6 \times 1.25 = 0.75\).

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Key Concepts

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

Uniform Distribution
A uniform distribution is a type of probability distribution where every outcome is equally likely within a specified interval. This means if you pick any point within this range, the probability of it occurring is the same across the entire interval. Unlike other distributions, such as the normal distribution, where some outcomes are more likely than others, a uniform distribution provides no such preferences.

For example, if we were talking about rolling a standard die, each number (1 through 6) would be considered part of a uniform distribution because they all have an equal chance of appearing. In a similar way, the length of the cutting blade in the exercise follows uniform distribution within 74.6 and 75.4 millimeters.

The probability density function for this uniform distribution is constant, meaning that throughout our interval, this function will provide a continuous and even measure of likelihood, demonstrated as 1.25 in this case. Understanding this helps simplify the calculation of probabilities because each segment within the range has the same density, making computations straightforward.
Probability Calculation
Probability calculation for a uniform distribution requires understanding of sub-intervals within the overall range. Each sub-interval's probability is proportional to its length compared to the entire range.

In the given exercise, we calculate the probability by multiplying the length of the interval by the probability density function, which is always 1.25 given, within the specified range. For example, to compute the probability of a blade being less than 74.8 millimeters, you identify the sub-interval from 74.6 to 74.8. This sub-interval's length is 0.2 millimeters. By multiplying 0.2 by the density 1.25, you find the probability for that segment as 0.25.

Similarly, if the problem involves two separate ranges, such as finding the probability of an outcome in "either this or that" situation, like "either less than 74.8 or greater than 75.2," calculate each part separately and add them together. This ensures that all possibilities are accounted for in the overall probability, such as 0.25 from each sub-interval in the example, summing up to a total probability of 0.5.
Specifications Compliance
Specifications compliance involves determining the probability or proportion of outcomes that meet defined specifications or criteria.

In manufacturing or similar processes, products must often fall within certain specifications to be considered valid. In the exercise, this range is given as 74.7 to 75.3 millimeters. This range ensures the cutting blades are neither too short nor too long, meeting quality standards.

To find the proportion of blades meeting this specification, determine the length of the interval (75.3 - 74.7 = 0.6 millimeters) and calculate the probability by multiplying with the density function, 1.25. This results in a probability or compliance rate of 0.75, indicating that 75% of the blades are expected to meet the specifications. Understanding specification compliance is crucial in ensuring quality and reliability in product outcomes, helping to maintain consistency across manufacturing.

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