The following table gives the literacy rate (in percentage) of 35 cities. Find the mean literacy rate.
Literacy rate (in %): | 45-55 | 55-65 | 65-75 | 75-85 | 85-95 |
Number of cities: | 3 | 10 | 11 | 8 | 3 |
We may calculate class marks (xi) for each interval by using the relation
xi = 
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 (fi) | xi | di = xi - 70 | ui = | fiui |
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 | ∑fiui = -2 |
Mean (x̅) = A + 
* h
= 70 + 
* 10
= 70 – 0.57
= 69.43
So, mean literacy rate is 69.437
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