f(2)=dF(=)={+)2.2> 10. otherwise W=min(x, y, then W=1/z, 0<w<l and w===w2 max(X, r 2 dhn1y2+m2s0+)0< so that fw(w)=/(/w)_I 0. otherwise eZo odz does not converge E{W}=,-"、,h=1/3 E{∠W}=E{ r max(X, r) min(X, y) nin(X, r) max(rri= 5. X and y are independent with exponential densities fx(xr=e-u(x), f(=e-u(y). Z=X+Y and W=X/. (18)f2(x)=? (a)e-l(=) (b) (-1) u(z (c)zeu(z) (d)(z-1)e(2-(z-1) (19)fm()=?7 2 2 , 1, (1 ) 0, otherwise. ( ) ( )/ Z Z z f z dF z dz z        min( , ) max( , ) X Y X Y W  , then W 1/Z, 0w1 and 2 21 | | | | dw w dz z   so that 1 2 2 2 2 (1 1/ ) 2 , 0 1, (1/ ) (1 ) | / | 0, otherwise. ( ) W w w f w w w dw dz f w            1 2 2 (1 ) { } zz E Z dz    does not converge. 10 2 2 (1 ) { } 1/3 ww E W  dw    . E{ZW}E{ max( , ) min( , ) X Y X Y min( , ) max( , ) X Y X Y  }1. 5. X and Y are independent with exponential densities ( ) ( ), ( ) ( ). x y X Y f x e u x f y e u y     Z=X+Y and W=X/Y. (18) ( ) Zf z ? (a) ( ) z e u z  (b) ( 1) ( 1) z e u z    (c) ( ) z ze u z  (d) ( 1) ( 1) ( 1) z z e u z     (e) None. (19) ( ) Wf w ?