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The table shows the age distribution in years of a group of people  Age(in years) …

The table shows the age distribution in years of a group of people 

Age(in years)  1 – 5 6 – 10 11 – 15 16 – 20 21 – 25 26 – 30
Number of people 18 12 25 15 20 10

Using an assume mean of 13 years, find the mean age of the people. 

Explanation
Age Class Mark(x) Freq(f)  d  = x – A Fd
1 – 5 3 18 -10 -180
6 – 10 8 12 -5 -60
11 – 15 13 25 0 0
16 – 20 18 15 5 75
21 – 25 23 20 10 200
26 – 30 28 10 15 150
Total    100   185

 

Where A is the assumed mean = 13

substituting, mean = 13 + (frac{18}{100}) = 13 + 1.85 

= 14.85 years