Verified answer

C.I Frequency

0-5 = 1

5-10 = 7

10-15= 11

15-20 = ? ( let it be m)

20-25 = ? ( let it be n)

25-30 = 4

30-35 = 2

[tex] \blue{total = > 40}[/tex]

[tex]25 + m + n = 40 \\ \red{ \boxed{m = 15 - n}} - - (1)[/tex]

Now,

1) Find Xi ( the mid value of C.I) of each class.

2) Multiply Xi by frequency

[tex] \green{example - - }[/tex]

Xi of 15-20 is 17.5

Multiply it with frequency

=> 17.5m

3) Find all such products and add them

4) Use equation (1) to convert 'm' into 'n'

5) Apply formula and just put values