class interval 
Frequency 
Cumulative frequency 
0  10 
5 
5 
10  20 
25 
30 (F) 
20  30 
x (f) 
30 + x 
30  40 
18 
48 + x 
40  50 
7 
55 + x 

N = 55 + x 

Given,
Median = 24
Then median class = 20  30
l = 20, h = 10, f = x and F = 30
Median = l + \(\frac{\frac{N}{2}F}{f}\)
\(24 = 20+\frac{55+\frac{x}{2}30}{x}\times10\)
4x = 275 + 5x – 300
4x – 5x = 25
x = 25
x = 25
Therefore,
missing frequency = 25