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If the mean $\mu$ of the data is 75, and the standard deviation $\delta$ is 5, how common is a value between 70 and 75?
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P(X<70) Z = x - μ / σ

= 70-75 / 5

= -1

P(X<75) Z = x - μ / σ

=75 - 75 / 5

= 0

P(-1 <= Z <= 0) = 0.5 - 0.15866

= 0.34134

≈ 34.13%
by Wooden (786 points)

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