Find arithmetic mean of the following frequency distribution by step deviation method.
1.Choose an arbitrary constant 'a'. (also called assumed mean)
2. xi = Upper limit+Lower limit2
3. Subtract the value of 'a' from xi.
4. The reduced value of (xi−a) is called the deviation of xi from 'a'.
5. Divide the deviation by constant where 'h' is the width of the class interval.
Let the assumed mean be a = 20 and h = 5
N=322,a=20,h=5 and ∑fiui=−59