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hyuki0000/a.rb

Created August 23, 2017 07:16
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N人のうち1人が100点でN-1人が0点であるとき、100点の人の偏差値
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a.rb
# N人のうち1人が100点でN-1人が0点であるとき、100点の人の偏差値
N = 15802 # 人数
μ = 100.0 / N # 平均
v = ((N-1) * (0-μ) ** 2 + 1 * (100-μ) ** 2) / N # 分散
σ = Math.sqrt(v) # 標準偏差
puts 50 + (100-μ) / σ * 10 # 100点の人の偏差値
# => 1307.0202862324857
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cf. https://twitter.com/arakencloud/status/899919837606027264

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