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  • The word ‘Data’ means information.
  • Statistical data are of two types. They are primary data and secondary data. 
  • The number of times an observation occurs is called the frequency of the observation. 
  • The Graphical representation of datas are Bar Graph , Histogram and Frequency Polygon. 
  • A bar graph is a pictorial representation of the numerical data by a number of bars (rectangles) of uniform width horizontally or vertically with equal spacing between them .Each rectangle or bar represents only one value of the numerical data. The height or length of the bars indicates on a suitable scale the corresponding value of the numerical data. 
  • A histogram or frequency histogram is a graphical representation of a frequency distribution in the form of rectangles with class intervals as bases and heights proportional to corresponding frequencies such that there is no gap between any two successive rectangles. 
  • A frequency polygon of a given frequency distribution is another method of representing frequency distribution graphically. 
  • The three measures of central tendency for ungrouped data are : 
  • Mean: It is given by adding all the values of the observations and dividing it by the total number of observations. It is denoted as . Therefore, . For an ungrouped frequency distribution
  • Median: It is the value of the middle most observation. If n is odd, the median = value of the()th
    observation. If n is even, Median = Mean of the values of the ()th and ( +1)th observations . 
  • Mode: The mode is the most frequently occurring observation

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