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Worked Examples · Example 15

Q.For the same continuous distribution (Example 13), calculate the standard deviation by the step-deviation method, taking deviations from 40 and dividing by the common factor 5.

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With A=40A = 40, c=5c = 5: ∑fd′=4\sum fd' = 4, ∑fd′2=472\sum fd'^2 = 472, so σ=11.79×5=17.168\sigma = \sqrt{11.79} \times 5 = 17.168.

Working table (with d=m−40d = m - 40 and d′=d5d' = \dfrac{d}{5}).

C.I.fmd = m − 40d′ = d ÷ 5fd′fd′²
10–20515−25−5−25125
20–30825−15−3−2472
30–5016400000
50–70860+20+4+32128
70–80375+35+7+21147
Total40+4472

Standard deviation (multiply back by the common factor c=5c = 5). …

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