P_PracticeExam6_05-1..
P_PracticeExam6_05-1..
P_PracticeExam6_05-1..
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26. For a Poisson random variable N with mean ! find<br />
lim E( N N # 1).<br />
!"0<br />
!"0<br />
n=1<br />
!"0<br />
n=1<br />
PRACTICE EXAMINATION NO. 6<br />
A. !<br />
Solution.<br />
B. 0 C. 1 D. e E. Cannot be determined<br />
n<br />
!<br />
Let fN ( n)<br />
=<br />
n! " e#! for n = 0,1,2,… be the probability function of this random variable. We<br />
have<br />
+%<br />
+% fN ( n)<br />
lim E( N N # 1)<br />
= lim&<br />
n $ f n N # 1<br />
!"0<br />
N N #1 ( ) = lim&<br />
n $ =<br />
Pr N # 1<br />
Answer C.<br />
= lim<br />
+%<br />
&<br />
!"0<br />
n=1<br />
( )<br />
( )<br />
fN n<br />
n $<br />
1' fN 0<br />
1<br />
= lim<br />
!"0 1' fN 0<br />
!<br />
= lim<br />
!"0 1' e '!<br />
( )<br />
+%<br />
&<br />
n=0<br />
=<br />
1<br />
= lim<br />
!"0 1 ' fN 0<br />
n $ f N n<br />
lim<br />
de l'Hospital !"0<br />
( ) =<br />
( )<br />
n $ fN ( n)<br />
=<br />
( ) n=1<br />
E( N )<br />
1 ' fN ( 0)<br />
=<br />
ASM Study Manual for Course P/1 Actuarial Examination. © Copyright 2004-2007 by Krzysztof Ostaszewski - 281 -<br />
lim<br />
!"0<br />
1<br />
= <strong>1.</strong> '!<br />
e<br />
27. X is a normal random variable with mean zero and variance 1<br />
and Y is distributed<br />
2<br />
exponentially with mean <strong>1.</strong> X and Y are independent. Find the probability Pr Y > X 2 ( ).<br />
1 e<br />
A. B. C.<br />
e<br />
!<br />
Solution.<br />
We know that<br />
1<br />
fX ( x)<br />
=<br />
1<br />
2 2!<br />
e<br />
for !" < x < +", and<br />
! y<br />
fY ( y)<br />
= e<br />
for y > 0, so that<br />
" 1<br />
#<br />
2<br />
&<br />
%<br />
%<br />
2 %<br />
$<br />
%<br />
x (<br />
(<br />
1 (<br />
2 '<br />
(<br />
fX,Y ( x, y)<br />
= 1<br />
! e" x2 " y<br />
e<br />
+%<br />
&<br />
1 1 2<br />
D. E.<br />
2!<br />
2<br />
2<br />
= 1<br />
! e" x2