Age in years (x) | No. of persons (f) | C.F. |
0-10 | 5 | 5 |
10-20 | 25 | 30 |
20-30 | x | 30 +x |
30-40 | 18 | 48 +x |
40-50 | 7 | 55 +x |
| N=55+x |
|
As, N=55+x ⇒N2=55+x2
Median=l+N2+Cf×h
As median is given 24, therefore median class is 20−30.
Therefore,
l=lower limit of median class =20
C=C.F. of the class preceding the median class =30
h= higher limit - lower limit =40−30=10
f=frequency of median class =x
∴median=20+55+x2−30x×10
24=20+x−52x×10
4=x−5x×5
⇒4x=5x−25
⇒x=25
Hence, the missing frequency is 25.