Let us find class marks (xi) for each interval by using the relation.
Class mark (xi) =
Now we may compute xi and fixi as follows:
Fro, the table we may observe that,
∑fi = 20
∑fixi = 162
Mean, X̅ =
= = 8.1
So mean number of plants per house is 8.1
We have used for the direct method values xi and fi are very small.
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