Question

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​

Answer 1

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