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Question
X is a normally distributed variable with mean µ = 30 and standard deviation σ = 4. Find P(X > 21)
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Solution
Given X ~ N(µ, σ2)
µ = 30
σ = 4
P(X > 21) = `"P"("Z" > (21 - 30)/4)`
= P(Z > – 2.25)
= 0.5 + P(– 2.25 < Z < 0)
= 0 5 + P(0 < Z < 2.25)
= 0.5 + 0.4878
= 0.9878
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