Lesson 11 · Comparison of Two Data using Whisker Box Plot
Mean Deviation
Optional MathematicsSubject
8 minEstimated read
Activity 1
Mean deviation of marks from the mean
Method
In a school, the marks obtained by students in a mathematics test of 75 full marks are: 10 - 20: 5 students, 20 - 30: 7 students, 30 - 40: 8 students, 40 - 50: 10 students, 50 - 60: 6 students, 60 - 70: 4 students.
(a) Find the values from the given data and fill in the table below.
(b) Find the mean deviation from the mean.
(c) Find the coefficient of mean deviation.
Marks
Number of students (f)
Mid-value (m)
fm
D = m - X̄
|D| = |m - X̄|
f|D|
10 - 20
5
20 - 30
7
30 - 40
8
40 - 50
10
50 - 60
6
60 - 70
4
N =
Σfm =
Σf|D| =
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