This Exam P sample reference tests Density Normalization. Normalizing the density gives a survival function of (1+x²)⁽⁻⁸⁾. Setting that survival probability to 0.98 gives the 2nd percentile 0.050284, so choice D is correct.
These notes identify the calculation error associated with each wrong letter when that error is reproducible.
AThis reports t²=0.98⁻¹⁄⁸-1=0.00252853, which rounds to 0.003, and forgets the final square root.
BThis reports the percentile probability 0.020 itself instead of solving F(t)=0.020 for a loss value.
CThis changes the survival exponent to 10 during integration: √(0.98⁻¹⁄¹⁰-1)=0.044970, which rounds to 0.045; the correct exponent is 8.
EThis omits the normalizing constant and sets [1-(1+t²)⁻⁸]/16=0.02, producing t=√(0.68⁻¹⁄⁸-1)=0.222236.
Original practice · fully worked
Original variant: conditional remaining stress
A component's nonnegative stress index Y has survival function S(y)=(1+y)⁽⁻³⁾. Inspection shows that the component has already exceeded stress level 1. Calculate the conditional median of the remaining excess Y-1.
A 0.260
B 0.414
C 0.520
D 0.828
E 1.000
Variant answer in brief
Conditioning above level 1 changes the excess survival function to [2/(2+m)]³. Setting it equal to one half gives m=2(2⁽¹⁄³⁾-1)=0.519842, so choice C is correct.
Setup
Setup
Let R=Y-1 after conditioning on Y>1. Express the tail of R as a ratio of the original survival probabilities.
Pr(R>r∣Y>1)=S(1)S(1+r)
Model
Model
A continuous conditional median leaves one half of the conditional distribution above it.
S(1)S(1+m)=(2+m2)3=21
Compute
Compute
Invert the conditional survival equation.
2+m2=2−1/3
m=2(21/3−1)=0.5198420998…
Answer
Answer
The conditional median remaining excess rounds to 0.520.
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