First, find the assumed mean 'A' from the midpoints, then calculate deviations 'd' and step-deviations 'd' ' by dividing by the class interval. Apply the formulas: Mean = A + (∑fd' / ∑f) * h, and Standard Deviation = h * √[(∑fd'²/∑f) - (∑fd'/∑f)²]. My daughter's old math notebook is propped next to my stationery box—I borrowed it last night to practice these exact sums before my mock test. It's the only quiet time I get, after shutting the salon and before she comes home from college.
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