The marks obtained by 60 students in an examination are as follows. Find the mean mark
marks
0-10
10 - 20
20 - 25
25 - 30
30 - 35
35 - 40
no.of students
3
8
20
16
9
4.
Answers
Answered by
1
Answer:
ANSWER
C-I F x Fx Step deviation d=
c
x−A
d
2
fd fd
2
5-15 8 10 80 -2 4 -16 32
15-25 12 20 240 -1 1 -12 12
25-35 20 30 600 0 0 0 0
35-45 10 40 400 +1 1 +10 10
45-55 7 50 350 +2 4 +14 28
55-65 3 60 180 +3 9 +9 27
n=60 Σ=1850 Σfd=+5 Σfd
2
=109
The mid-point of class intervals have C=10 as a common factor and the mean is not an integer.
∴ Let us follow step deviation method.
(i) Mean=
n
∑fx
=
60
1850
=30.8
(ii) S.D=
n
∑fd
2
−(
n
∑fd
)
2
×C=
60
109
−(
60
5
)
2
×10=
1.81
×10=1.34×10,σ=13.4.
This means, on an average each score deviates from the mean value 30.8 by 13.4.
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