Frequency Polygon


 
 
Concept Explanation
 

Frequency Polygon

Frequency Polygon: 

It is another method of representing frequency distributions graphically. Also, it is used to represent classified or grouped data graphically.  It is a line graph of grouped frequency distribution plotted between class marks and frequencies. It can be obtained in two ways

  • (a) By first drawing Histogram and
  • (b) Without drawing Histogram
  • Steps of Drawing Drawing Frequency Polygon (By First Drawing Histogram) :

  • (i) Draw the histogram from the given data
  • (ii) Obtain the mid - points of the upper horizontal sides of each rectangle.
  • (iii) Join these mid-points of the adjacent rectangles by dotted line segments.
  • (iv) Obtain the mid-point of two assumed class intervals of zero frequency. One before the first and other after the last class interval.
  • (v) Complete the polygon by joining the mid-point of class first to mid-point of its left adjacent class and mid-point of last class intervals to the mid point of its right adjacent class interval.
  • Illustration : Draw a histogram and a frequency polygon of the following data :

    Age in years 0-6 6-12 12-18 18-24 24-30 30-36 36-42
    No. of persons 6 11 25 35 18 12 6

    Solution : First we draw histogram of the given data, then we will locate mid-point of top horizontal side of rectangles.

    Now,  join these mid points by dotted line segments. Complete the polygon by joining the mid points of first interval to the mid-point of its left adjacent assumed class interval of zero frequency and mid-point of last class interval to its adjacent right assumed class interval of zero frequency.

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    Sample Questions
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    Question : 1

    If the weight range for a class of 45 students is distributed by 35 - 45, 45 - 55, 55 - 65, 65 - 75. What would be the class marks for each weight range ?

    Right Option : A
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    Explanation
    Question : 2

    When successive mid-points in a histogram are connected by straight lines, the graph is called a _____________

    Right Option : D
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    Explanation
    Question : 3

    In a cumulative frequency polygon, frequencies are plotted against

    Right Option : B
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    Explanation
     
     
     


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