We may calculate class marks (x_{i}) for each interval by using the relation
x_{i} \(=\frac{Upper\,class\,limit+lower\,class\,limit}{2}\)
Class size (h) for this data = 10
Now taking 70 as assumed mean (A) we can calculate as follows:
Literacy rate (in %) 
Number of cities (f_{i}) 
x_{i} 
d_{i} = x_{i}  70 
u_{i} = \(\frac{di}{10}\) 
f_{i}u_{i} 
45  55 
3 
50 
20 
2 
6 
55  65 
10 
60 
10 
1 
10 
65  75 
11 
70 
0 
0 
0 
75  85 
8 
80 
10 
1 
8 
85  95 
3 
90 
20 
2 
6 

N = 35 



\(\sum\)f_{i}u_{i} = 2 
Mean (x̅) = A + \(\frac{\sum f_iu_i}{N}\times h\)
\(=70+\frac{2}{35}\times10\)
\(=700.57\)
= \(69.43\)
So,
mean literacy rate is 69.437