For calculating the mode of the grouped data graphically, the following procedure is adopted.
Draw a histogram of the data; the modal class is the tallest rectangle.
Draw a line from the top right corner of the tallest rectangle to the top right corner of the preceding rectangle.
Draw a line from the top left corner of the tallest rectangle to the top left corner of the succeeding rectangle.
Draw a line perpendicular to the X-axis from the point of intersection of lines drawn in steps 2 and 3. The point of intersection of the perpendicular line with the X-axis represents the mode.
Example
Let us calculate the Mode using the graphical method for the following distributions:
Gross profits as percentage of sales
0-7
7-14
14-21
21-28
28-35
36-42
42-49
Number of companies
19
25
36
72
51
43
28
Using the procedure described above, we draw the histogram and other lines for the calculation of mode. The mode is 25.