/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 46 Suppose that the probability den... [FREE SOLUTION] | 91Ó°ÊÓ

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Suppose that the probability density function of the length of computer cables is \(f(x)=0.1\) from 1200 to 1210 millimeters. (a) Determine the mean and standard deviation of the cable length. (b) If the length specifications are \(1195

Short Answer

Expert verified
Mean is 1205 mm, standard deviation is approx. 2.89 mm, and 50% of cables meet specifications.

Step by step solution

01

Understanding the Uniform Distribution

The probability density function given, \( f(x) = 0.1 \), is constant in the interval from 1200 to 1210 millimeters. This is a uniform distribution because each outcome in this interval is equally likely.
02

Calculate the Mean for Uniform Distribution

For a uniform distribution on the interval \([a, b]\), the mean (expected value) \( \mu \) is given by \( \mu = \frac{a + b}{2} \). Here, \( a = 1200 \) and \( b = 1210 \). Thus, \( \mu = \frac{1200 + 1210}{2} = 1205 \) mm.
03

Calculate the Standard Deviation for Uniform Distribution

For a uniform distribution on the interval \([a, b]\), the standard deviation \( \sigma \) is given by \( \sigma = \frac{b - a}{\sqrt{12}} \). Here, \( a = 1200 \) and \( b = 1210 \). Thus, \( \sigma = \frac{1210 - 1200}{\sqrt{12}} = \frac{10}{\sqrt{12}} \approx 2.89 \) mm.
04

Determine Proportion Within Specifications

The specifications are for lengths between 1195 and 1205 mm. The uniform distribution is defined from 1200 to 1210 mm. Calculate the area within the overlap region of \([1200, 1205]\): The proportion is \( \frac{1205 - 1200}{1210 - 1200} = \frac{5}{10} = 0.5 \).
05

Conclusion

The mean length of the cables is 1205 mm, the standard deviation is approximately 2.89 mm, and 50% of the cables are within the given specifications.

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Key Concepts

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

Probability Density Function
In a uniform distribution, the probability density function (PDF) indicates that every outcome within a given interval is equally likely. The given PDF, where \( f(x) = 0.1 \) for cable lengths between 1200 mm and 1210 mm, exemplifies this. It is crucial to understand that this 0.1 represents the height of the uniform distribution over the interval. The complete range of values can be represented as a flat, horizontal line in a probability density plot. This height ensures that the total area under the curve within the specified interval equals 1, fulfilling the requirement that the total probability of all outcomes sums up to 1.
An important characteristic of a uniform distribution is that it relies heavily on the range of values. In this case, the range is 10 mm, from 1200 to 1210. However, any value outside this interval would naturally have a probability of zero since they are not included in the specified interval.
Understanding the PDF for a uniform distribution simplifies the calculation of probabilities across intervals, where proportions can be easily calculated by comparing sub-intervals to the total interval length.
Mean and Standard Deviation Calculation
Calculating the mean and standard deviation for a uniform distribution is straightforward once you grasp the mathematical formulas used.
For the mean of a uniform distribution, it is always halfway between the upper and lower bounds of the interval. Calculated as \( \mu = \frac{a + b}{2} \), this formula ensures that the mean represents the central point of the distribution. With our example, the interval being 1200 to 1210, the mean is \( 1205 \) mm. This value represents not only the central tendency but also the balance point of the distribution.
In contrast, the standard deviation for a uniform distribution captures the spread of values around the mean. Computed by \( \sigma = \frac{b - a}{\sqrt{12}} \), this equation acknowledges that values are equally dispersed across the entire range. For our cable lengths, the calculation, \( \frac{10}{\sqrt{12}} \approx 2.89 \) mm, suggests a standard deviation that, although not large, underscores the uniform spread of potential cable lengths. Thus, the mean and standard deviation of a uniform distribution give a quick snapshot of the distribution's balance and variability.
Specification Limits Proportion
Determining the proportion of outcomes within specific limits for a uniform distribution involves examining the overlap between desired specifications and the original distribution's interval.
For this problem, cable specifications are 1195 to 1205 mm, and we are considering the population of cables uniformly distributed between 1200 and 1210 mm. The overlap, or shared range, thus extends from 1200 to 1205 mm.
Computing the proportion within this overlap is simple by recognizing how much of the original interval is contained within the specifications. Calculated as \( \frac{1205 - 1200}{1210 - 1200} = \frac{5}{10} = 0.5 \), we ou find that 50% of cable lengths meet the specifications.
This method highlights the straightforward approach of using the length of overlap divided by the total interval length to easily find the proportion of values within any specification limits.

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