10
30: If the mean of the following data is 7.5. Then find the missing frequency 'x'.
Marks
5
6
7
8
9
No. of students
3
10
17
X
8
4
Answers
Answer:
X=18
Step-by-step explanation:
Marks (x1) No of students (f1) x1f1
5 3 15
6 10 60
7 17 119
8 X 8X
9 8 72
10 4 0
Total 42+X 306+8X
Sum of frequency (f1) =42+X
Sum of f1x1 = 306+8X
Given mean is 7.5
Mean
x
ˉ
=
Σf
1
Σf
1
x
1
∴7.5=
41+X
306+8X
⇒306+8X=7.5(42+X)
⇒306+8X=315+7.5X
⇒8X−7.5X=315−306
⇒0.5X=9
⇒X=18