720                                                    21

        ^+ $15
[(^- $90) + (1,05  $100)].    ,    -
   .       
     . ?     -
   ,    (   ,
 + $3 < , + $15).   ,     $12
[(^ + $15) - (^ + $3)]. ,      
 S&P  100 ,     90 .

     ,    -
     ,      .
        ,  -   -
   , ^ -     (.. /^ 
  ),        :

, + .

d      -    s

 R      ,   
    :

(,- ^)+ [(] + R)x ^].
     :

,+^(,- ^)+ [(1 + R)xP^].                  (21.11)
 , :

^-P^(R-y) ,,                           (21.12)


^-= ^+ RP^-yP^.                          (21.13)

 (21.12) ,       
    : (1)    ^; (2) 
         
R - .           
        .    -
     .      ^.
 (21.13) ,       -
      ,     (21.4),
   ()  . ,    -
 (/),   RP^,      () -   ^. -
   :

 = RP^ - ,-                      (21.14)

  ,    R    
 .      .

      5%,   - 3%,  -
 S&P 500- 100.  ,      -
  S&P 500    S&P 500  2 [(0,05 - 0,03)  100]. -
,    ,  S&P 500  100, 
102,     2.    ,    
  ,        
2,5% (5%/2)  1,5% (3%/2).      1 [(0,025  0,015)
 100],  ,   S&P 500      100.