Multiple bar charts, also known as grouped or clustered bar charts, are used to display and compare values across different categories for multiple data series simultaneously. By placing bars side-by-side for each category, they allow for an immediate visual comparison of the magnitude of different data sets.

A frequency distribution is a tabular summary of data showing the frequency (or number) of items in each of several non-overlapping classes. It is a fundamental tool in descriptive statistics used to organize raw data into a more interpretable format, allowing for the identification of patterns, central tendencies, and the spread of the data set.

The class interval, often referred to as the class width or size, is calculated as the difference between the upper class limit and the lower class limit of a specific class. It represents the range of values that fall within a particular category in a frequency distribution table.

A two-way table, or contingency table, is used to display the relationship between two categorical variables. It organizes data into rows and columns, allowing for the analysis of interrelated characteristics within the dataset.

Before constructing a frequency distribution, one must first decide on the range and the number of classes. Selecting appropriate class intervals is the foundational step that dictates how the data will be grouped and summarized, ensuring that the resulting distribution accurately reflects the underlying data structure.

In graphical representation, two-dimensional diagrams are those where both length and breadth are used to represent data values. Examples include rectangles, squares, and pie charts, which are often referred to as area or surface diagrams because the area of the shape is proportional to the magnitude of the data.

Repository tables, often referred to as general-purpose or reference tables, are designed to store large amounts of data in a systematic and orderly fashion for future reference. Unlike summary tables, which focus on specific analytical findings, repository tables provide a comprehensive view of the dataset, allowing researchers to extract various details as needed for different statistical analyses.

Marginal frequencies are the totals of the rows or columns in a contingency table. They represent the frequency distribution of one variable while ignoring the other variable, calculated by summing across the joint distribution.

The class interval width is calculated by finding the range of the data (Maximum - Minimum) and dividing it by the desired number of classes. Here, the range is 60 - 40 = 20. Dividing the range (20) by the number of classes (5) results in a class interval width of 4.

A 'less than' cumulative frequency distribution is constructed by adding the frequencies of each class interval to the sum of the frequencies of all preceding intervals. This represents the total number of observations that are less than the upper boundary of a given class interval, starting from the lowest value.