By direct method
Class interval 
Mid value (x_{i}) 
Frequency (f_{i}) 
f_{i}x_{i} 
1  4 
2.5 
6 
15 
4  9 
6.5 
12 
78 
9  16 
12.5 
26 
325 
16  27 
21.5 
20 
430 


N = 64 
\(\sum\)f_{i}u_{i} = 848 
Mean \(=\frac{\sum f_ix_i}{N}+A\)
\(=\frac{848}{64} = 13.25\)
By assumed mean method
Let,
the assumed mean (A) = 6.5
Class interval 
Mid value (x_{i}) 
u_{i} = x_{i } A = x_{i}  6.5 
Frequency (f_{i}) 
f_{i}u_{i} 
1  4 
2.5 
4 
6 
24 
4  9 
6.5 
0 
12 
0 
9  16 
12.5 
6 
26 
156 
16  27 
21.5 
15 
20 
300 



N = 64 
\(\sum\)f_{i}u_{i} = 432 
Mean = A + \(\frac{\sum f_iu_i}{N}\)
\(=6.5+\frac{432}{64}\)
\(=6.5+6.75\)
\(=13.25\)