TOPICS
Formulae

1. Class Mark
Median = l + [(n/2 - cf)/f] x h
    
2. The mean of grouped data
(i) Direct Method: x = Σfixi/Σfi

(ii) Assumed mean method: x = a + Σfidi/Σfi

(iii) Step-deviation method: x = a + (Σfiui/Σfi) x h

where a = assumed mean,
Σfi or n = number of observations,
h = class size (assuming class size to be equal).
    
3. The mode of grouped data
Mode = l + [(f1 - f0)/(2f1 - f0 - f2)] x h

where l = lower limit of the modal class,
h = size of the class interval (assuming all class sizes to be equal),
f1 = frequency of the modal class,
f0 = frequency of the class preceding the modal class,
f2 = frequency of the class succeeding the modal class.
    
4. The median of grouped data
Median = l + [(n/2 - cf)/f] x h

where l = lower limit of median class,
n = number of observations,
cf = cumulative frequency of class preceding the median class,
f = frequency of median class,
h = class size (assuming class size to be equal).
    
5. Relationship between Mean, Mode & Median
3 Median = Mode + 2 Mean
    
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