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Flip to reveal answersWhat does the inverse normal do?
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All 9 Flashcards — Inverse normal
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Question
What does the inverse normal do?
Answer
Given a left-tail probability P(X < x), it returns the value x.
Question
What GDC command finds x from a probability?
Answer
invNorm(area, μ, σ), where area is the left-tail probability.
Question
Which tail does invNorm use?
Answer
The left (lower) tail — the area to the left of x.
Question
How do you find x when P(X > x) = p?
Answer
Use the left area 1 − p: x = invNorm(1 − p, μ, σ).
Question
For the central c% of data, what are the tail areas?
Answer
Each tail is (1 − c)/2; use those areas in invNorm.
Question
How do you find an unknown σ from a probability?
Answer
Find z = invNorm(p, 0, 1), then σ = (x − μ)/z.
Question
How do you find an unknown μ from a probability?
Answer
Find z = invNorm(p, 0, 1), then μ = x − zσ.
Question
Why use z (μ=0, σ=1) when σ is unknown?
Answer
invNorm needs σ to return x directly; with σ unknown you must work through the standardised z.
Question
If P(X < a) = 0.1, what is the sign of z?
Answer
Negative — a left-tail probability below 0.5 gives a negative z.
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Full study notes for Inverse normal
Topic 4.12 hub
z-values & inverse normal
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Math AA SL exam skills
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