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Flip to reveal answersWhat does X ~ N(μ, σ²) mean?
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All 9 Flashcards — Normal probabilities
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Question
What does X ~ N(μ, σ²) mean?
Answer
X is normally distributed with mean μ and variance σ² (so standard deviation σ).
Question
What shape is the normal distribution?
Answer
A symmetric bell curve centred on the mean.
Question
What does normalcdf(lower, upper, μ, σ) give?
Answer
The probability P(lower < X < upper) — the area under the curve between the bounds.
Question
How do you find P(X < a) on the GDC?
Answer
normalcdf with a very small lower bound (e.g. −1E99) and upper bound a.
Question
How do you find P(X > a)?
Answer
normalcdf with lower bound a and a very large upper bound (e.g. 1E99).
Question
What is P(X < μ)?
Answer
0.5 — half the area is below the mean.
Question
State the 68–95–99.7 rule.
Answer
About 68% of data lies within 1σ of the mean, 95% within 2σ, 99.7% within 3σ.
Question
How do you find an expected number from a normal probability?
Answer
Multiply the probability (normalcdf) by the total number of items.
Question
In N(150, 20²), what is σ?
Answer
20 (the variance is 400; the GDC needs σ = 20).
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Topic 4.9 hub
Normal distribution
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