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The accompanying frequency distribution of fracture strength (MPa) observations for ceramic bars fired in a particular kiln appeared in the article "Evaluating Tunnel Kiln Performance" (Amer. Ceramic Soc. Bull., Aug. 1997: 59-63). \(\begin{array}{lcccccc}\text { Class } & 81-<83 & 83-<85 & 85-<87 & 87-<89 & 89-<91 \\ \text { Frequency } & 6 & 7 & 17 & 30 & 43 \\ \text { Class } & 91-<93 & 93-<95 & 95-<97 & 97-<99 \\ \text { Frequency } & 28 & 22 & 13 & 3\end{array}\) a. Construct a histogram based on relative frequencies, and comment on any interesting features. b. What proportion of the strength observations are at least 85 ? Less than 95 ? c. Roughly what proportion of the observations are less than \(90 ?\)

Short Answer

Expert verified
a) Construct a histogram using relative frequencies. b) Proportion ≥ 85: ~0.87; Proportion < 95: ~0.92. c) Proportion < 90: ~0.61.

Step by step solution

01

Understand the Data

Examine the given frequency distribution which details the classes and respective frequencies for fracture strength (MPa) observations of ceramic bars. This data needs to be translated into relative frequencies for histogram construction.
02

Calculate the Total Frequency

Sum the frequencies of all classes: \(6 + 7 + 17 + 30 + 43 + 28 + 22 + 13 + 3 = 169\). This total frequency will be used to calculate relative frequencies.
03

Determine Relative Frequencies

Calculate the relative frequency for each class by dividing each class frequency by the total frequency. For example, for the class '81-<83', the relative frequency is \(\frac{6}{169}\). Repeat for other classes.
04

Construct Histogram

Using the relative frequencies calculated, generate a histogram. The x-axis should represent the fracture strength intervals, and the y-axis should represent the relative frequencies.
05

Analyze the Histogram

Identify any trends or interesting features in the histogram, such as symmetry, skewness, or any apparent outliers.
06

Calculate Proportion of Observations ≥ 85

Observations at least 85 include classes from '85-<87' to '97-<99'. Sum their frequencies and divide by the total frequency: \((17 + 30 + 43 + 28 + 22 + 13 + 3) / 169\).
07

Calculate Proportion of Observations < 95

Observations less than 95 include classes from '81-<83' to '93-<95'. Sum their frequencies and divide by the total frequency: \((6 + 7 + 17 + 30 + 43 + 28 + 22) / 169\).
08

Calculate Proportion of Observations < 90

Observations less than 90 include classes from '81-<83' to '89-<91'. Sum their frequencies and divide by the total frequency: \((6 + 7 + 17 + 30 + 43) / 169\).

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Key Concepts

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

Frequency Distribution
Frequency distribution is a way to organize data into different intervals or "classes" to show how often each value or group of values appears. In the context of fracture strength observations for ceramic bars, the data is grouped into intervals such as '81-<83', '83-<85', etc. Each interval is then associated with a frequency, which tells us how many observations fall within that range. Understanding frequency distribution is crucial for analyzing data, as it provides a clear snapshot of the distribution of data points. Observing these distributions can help us identify patterns or trends, such as whether data is clustered around a particular value or if there are gaps. Frequency distributions simplify data handling by breaking down large amounts of information into concise and manageable parts.
Histogram
A histogram is a type of bar chart that visually represents the frequency distribution of a dataset. In a histogram, each bar represents an interval (also called a "bin"), and the height of the bar shows the frequency or relative frequency of data points within that range. In our exercise, fracture strength intervals like '81-<83', '83-<85', etc., can be plotted as bars. Creating a histogram involves plotting each class interval on the x-axis and using the calculated relative frequencies for each interval on the y-axis. This graphical representation allows us to easily see the shape of the distribution, identifying any trends, such as skewness, symmetry, or whether there are any outliers. Histograms are particularly useful for examining large datasets to see the overall pattern without getting caught up in individual data points.
Relative Frequency
Relative frequency provides a more normalized view of data by presenting the fraction of the total number of observations that fall within each class interval. It is calculated by dividing the frequency of a class by the total number of observations. For instance, if the class '81-<83' has a frequency of 6, and there are 169 total observations, the relative frequency is \( \frac{6}{169} \\).Relative frequencies are expressed as decimals or percentages and are particularly valuable when comparing datasets of different sizes. They help us understand how significant a particular class interval is relative to the entire dataset. When plotted on a histogram, relative frequencies allow for easy visual comparison between different intervals, making it easier to see the proportional distribution of data.
Proportion Calculation
Proportion calculation involves determining the ratio of a subset of data to the whole dataset. In the context of our exercise, it helps in discerning what portion of the ceramic bar observations fall into specific categories or conditions, such as being at least or less than a certain value (< 85 or ≥ 90, for example). To calculate these proportions, we sum the frequencies of the relevant classes and divide by the total number of observations. For instance, to find the proportion of observations with a strength of at least 85, we sum the frequencies from the class '85-<87' onward and divide by the total frequency of 169. Each proportion offers insight into data behavior under various conditions and ensures we can make informed decisions or predictions based on the data.

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