!George Austin Corbett, ENGR225, Thursday 1700-2000 lab. 
!Note this is NOT my code, but was pasted in from figure 1.8 of chapter 1 of Fortran 90 book
 
PROGRAM Radioactive_Decay
!----------------------------------------------------------------------------
! This program calculates the amount of a radioactive substance that 
! remains after a specified time, given an initial amount and its 
! half-life.  Variables used are:
!   InitalAmount    : initial amount of substance (mg)
!   HalfLife        : half-life of substance (days)
!   Time            : time at which the amount remaining is calculated (days)
!   AmountRemaining : amount of substance remaining (mg)
!
! Input:   InitialAmount, HalfLife, Time
! Output:  AmountRemaining
!-----------------------------------------------------------------------------
 
  IMPLICIT NONE
  REAL :: InitialAmount, HalfLife, Time, AmountRemaining
 
  ! Get values for InitialAmount, HalfLife, and Time.
 
  WRITE(*,*) "Enter initial amount (mg) of substance, its half-life (days)"
  WRITE(*,*) "and time (days) at which to find amount remaining:"
  READ *, InitialAmount, HalfLife, Time
 
  ! Compute the amount remaining at the specified time.
  AmountRemaining = InitialAmount * 0.5 ** (Time / HalfLife)
 
  ! Display AmountRemaining.
  PRINT *, "Amount remaining =", AmountRemaining, "mg"
 
END PROGRAM Radioactive_Decay
 

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