. In a retail market, fruit …

TEP DEVIATION METHOD:

Step deviation method is used in the cases where the deviation from the assumed mean 'A' are multiples of a common number. If the values of ‘di’ for each class is a multiple of ‘h’ the calculation become simpler by taking ui= di/h = (xi - A )/h

Here, h is the class size of each class interval.

★★ Find the class marks of class interval. These class marks would serve as the representative of whole class and are represented by xi.  

★★ Class marks (xi)  = ( lower limit + upper limit) /2

★★ We may take Assumed mean 'A’ to be that xi which lies in the middle of x1 ,x2 …..xn

MEAN = A + h ×(Σfiui /Σfi) , where ui =  (xi - A )/h

[‘Σ’ Sigma means ‘summation’ ]

FREQUENCY DISTRIBUTION TABLE

★★ Here,the frequency table is given in inclusive form. So we first change it into exclusive form by  subtracting and adding h/2 to the lower and upper limits respectively of each class ,where ‘h’ denotes the difference of lower limit of a class and upper limit of the previous class.

Here, h/2 = ½ = 0.5  

From the table : Σfiui = 25 ,  Σfi = 400

Let the assumed mean, A = 57,  h = 3

MEAN = A + h ×(Σfiui /Σfi)

Mean = 57 + 3 (25/400)

= 57 + 3 (1/16)

= 57 + 3/16

= 57 + 0.187

= 57.187

Mean = 57.19  (approximate)

Hence, the Mean number of mangoes kept in a packing box is 57.19  (approximate)