1. Measurement of central tendency of data.
Mean
1. Direct Method
2. Assumed Mean
Method
3. Step Deviation
Method
Median
Mode
Direct Method
Σ fixi
Σ fi
Step 1
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class interval
class mark
( xi )
frequency
( fi )
fixi
Total
Σ fi =
Σ fixi =
Step 2
Class width =
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No. of plants | 0 – 2 | 2 - 4 | 4 - 6 | 6 - 8 | 8 - 10 | 10 - 12 | 12-14 |
No. of houses | 1 | 2 | 1 | 5 | 6 | 2 | 3 |
Ex.14.1)1) 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.
Which method did you use for finding the mean and why?
Sol:
(class interval)
class mark
( xi )
frequency
( fi )
fixi
2 - 4
4 - 6
8 - 10
10 - 12
1
3
5
9
11
1
2
1
6
2
1
6
5
54
22
Total
--
Σ fi =
Σ fixi =
20
162
Σ fixi
Σ fi
=
162
20
=
8.1
Class width(h) =
2
12 - 14
3
8 - 10
7
5
35
13
39
What we need to find?
No. of plants
No. of houses
Class width (h) is found by subtracting two consecutive lower limits or two consecutive upper limits
0 - 2
8.1
1 x 1
3 x 2
5 x 1
7 x 5
9 x 6
11 x 2
13 x 3
Adding all fi
Adding all fixi
We used direct method
because the values of fi and xi are small .
Exercise – 14.1 – Q.1