Example to illustrate the sensitivity to discount/interest rates
P = $50,000 __1___
                   (1 + 0.06)8

      Ž SPPW
  = $50,000  | i = .06  |
      ‘  n = 8 ž

 = $50,000 (0.627)  = $31,350

For F = $50,000 and n = 8 if
i = 0.06           0.08          0.10

                    then P            $31,350      $27,000     $23,350