November 2001 - Course 1 SOA Solutions
November 2001 - Course 1 SOA Solutions
November 2001 - Course 1 SOA Solutions
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7. A<br />
Cov C , C = Cov X + Y, X + 1.2Y<br />
( 1 2) ( )<br />
= Cov ( X, X) + Cov ( Y, X) + Cov ( X,1.2Y) + Cov( Y,1.2Y)<br />
= Var X + Cov ( X, Y) + 1.2Cov ( X, Y)<br />
+ 1.2VarY<br />
= Var X + 2.2Cov ( X, Y)<br />
+ 1.2VarY<br />
( ) ( ( ))<br />
2<br />
( ) ( E Y )<br />
2 2<br />
2<br />
Var X = E X − E X = 27.4 − 5 = 2.4<br />
VarY<br />
2 2<br />
= E Y − ( ) = 51.4 − 7 = 2.4<br />
( X + Y) = X + Y + ( X Y)<br />
Var Var Var 2Cov ,<br />
1<br />
Cov ( XY , ) = Var ( X+ Y)<br />
−Var X−VarY<br />
2<br />
1<br />
= ( 8 − 2.4 − 2.4 ) = 1.6<br />
2<br />
Cov , = 2.4 + 2.2 1.6 + 1.2 2.4 = 8.8<br />
( C C ) ( ) ( )<br />
1 2<br />
( )<br />
<strong>Course</strong> 1 <strong>Solutions</strong> 4 <strong>November</strong> <strong>2001</strong>