(Q9). A survey was conducted by a group of students as a part of their environment awareness programme, in which they collected the following data regarding the number of plants in 20 houses in a locality. Find the mean number of plants per house.

Number of plants 0-2 2-4 4-6 6-8 8-10 10-12 12-14
Number of houses 1 2 1 5 6 2 3

Solution:

Number of plants(Class Interval) Number of houses(fi) Class marks (xi) fixi
0-2 1 1
2-4 2 3
4-6 1 5
6-8 5 7
8-10 6 9
10-12 2 11
12-14 3 13
Total ∑fi = 20 - ∑fixi =

Since fi and xi are of small values we use direct method.

∴ x̄ =
∑fixi
∑fi
 =
20
 = .1