The statement is False. According to the textbook context, while class intervals are generally of equal width, it is not essential. The text clearly states that 'in some type of data, it is convenient, at times necessary, to use varying width of class intervals.' An example provided is tabulating deaths by age, where shorter age intervals are used when death rates are high. In such cases, the height of the rectangle is calculated as the quotient of frequency and width of the class interval. Therefore, histograms can have rectangles with unequal widths when dealing with varying class intervals.