To find the class mark \\( \\left(x_{i}\\right) \\) for each interval, the following relation is used.
Class mark \\( \\left(x_{i}\\right) \\) \\( \\frac{\ ext { Upper class limit + Lower class limit }}{2} \\)
\\( x_{i} \ ext { and } f_{X_{i}} \\) can be calculated as follows
From the table it can be observed that
\\( \\sum f_{i}=20 \\)
\\( \\sum f_{r} x_{i}=162 \\)
Mean \\( \\overline{x}=\\frac{\\sum f_{f_{i}}}{\\sum f_{i}} \\)
\\( =\\frac{162}{20}=8.1 \\)
Therefore mean number of plants per house is 8.1 Here, direct method has been used as the values of class marks \\( \\left(x_{i}\\right) \\) and \\( f_{i} \\) are small