math.illinoisstate.edumath.illinoisstate.edu/krzysio/1-17-9-ko-exercise.pdf · an insurance company...
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Krzys’ Ostaszewski: http://www.krzysio.net Author of the “Been There Done That!” manual for Course P/1 http://smartURL.it/krzysioP (paper) or http://smartURL.it/krzysioPe (electronic) Instructor of online P/1 seminar: http://smartURL.it/onlineactuaryIf you find these exercises valuable, please consider buying the manual or attending the seminar, and if you can’t, please consider making a donation to the Actuarial Program at Illinois State University: https://www.math.ilstu.edu/actuary/giving/ Donations will be used for scholarships for actuarial students. Donations are tax-deductible to the extent allowed by law.
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Exercise for January 17, 2009
November 2000 Course 1 Examination, Problem No. 9, also Study Note P-09-08, Problem No. 70 An insurance company sells an auto insurance policy that covers losses incurred by a policyholder, subject to a deductible of 100. Losses incurred follow an exponential distribution with mean 300. What is the 95-th percentile of actual losses that exceed the deductible?
A. 600 B. 700 C. 800 D. 900 E. 1000
Solution. Let X stand for actual losses incurred. We are given that X follows an exponential distribution with mean 300, and we are asked to find the 95-th percentile of all claims that exceed 100. In other words, we want to find p95 such that
0.95 =Pr 100 < x < p95( )P X > 100( ) =
FX p95( ) − FX 100( )1− FX 100( ) ,
where FX is the cumulative distribution function of X. We know that FX x( ) = 1− e−x300 .
Therefore, we end up with this equation
0.95 =1− e
−p95300 − 1− e
−100300
⎛⎝⎜
⎞⎠⎟
1− 1− e−100300
⎛⎝⎜
⎞⎠⎟
=e−13 − e
−p95300
e−13
= 1− e13e
−p95300 .
The solution is given by e−p95300 = 0.05e
−13 , or
p95 = −300 ln 0.05e−13
⎛⎝⎜
⎞⎠⎟≈ 999.
Answer E.
© Copyright 2004-2009 by Krzysztof Ostaszewski.
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