Formulae for Mean of Grouped Data In The Form of Classes -
1) Direct Method –
Step 1. For each class, find the class mark xₐ by using the relations,
1
xₐ = -------- (lower limit + upper limit)
2
∑fₐdₐ
Step.2. Use the formulae, Mean = ----------
∑fₐ
2) Short Cut Method or Deviation Method –
Step 1. For each class, find the class mark xₐ
Step 2. Let A be the assumed mean.
Step 3. Find dₐ = (xₐ - A)
∑fₐdₐ
Step 4. Use the formulae, Mean = (A + ---------)
∑fₐ
3) Step Deviation Method -
Step 1. For each class, find the class mark xₐ
Step 2. Let A be the assumed mean
(xₐ - A)
Step 3. Calculate, uₐ = ----------, where c is the class size
c
∑fₐuₐ
Step 4. Use the formulae, Mean = (A + c. ---------)
∑fₐ
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