In: Statistics and Probability
I need the calculation of this problem. This question has solution but I can't figure the answer calculation
Again I need calculation probably last line
Question :
On a certain standardized test
Exactly 66% of the people who took the test scored higher than Mr. Peterson. Find a, b, and c such that Mr. Peterson's score is approximately
a + b ⋅ Φc(d)
Do not make a continuity correction.
What is a + b + 2bcd?
X is a random person’s score. X is approximately Normal(51,152).
x = Mr. Peterson’s score.
P(X > x) = 0.66
P((X − 51)/15 > (x − 51)/15) = 0.66 normalize
P(Z > (x − 51)/15) ≈ 0.66 approximate
1 − P(Z > (x − 51)/15) ≈ 1 − 0.66
P(Z ≤ (x − 51)/15) ≈ 0.34
?((x − 51)/15) ≈ 0.34
(x − 51)/15 ≈ ?−1(0.34)
x ≈ 51 + 15 ?−1(0.34)
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a+b+2bcd = 51+15+2*15*-1*0.34 = 55.8