printf/scanf and decimals

//program to determine equal spacing for pickets

#include <stdio.h>    //scanf & printf
#include <conio.h>    //getch
# include <ctype.h>    //toupper

#define TRUE 1
#define FALSE !TRUE

char stay_open,c;

float distance,width,pickets,spacing,last_space;

void main()
{
      stay_open = TRUE;
      while (stay_open)
      {
      printf("\nEnter distance between posts  ");  // 45.8399
      scanf ("%f",&distance);

      printf("\nEnter width of picket  ");
      scanf("%f",&width);                        //  1.5

      printf("\nEnter desired number of pickets  ");
      scanf("%f",&pickets);                          // 30

/*  The formula for determining how to evenly  space  pickets between 2 posts is:  */
      spacing = ( (distance - (pickets * width) )  / (pickets + 1) );

      /*  Using the above entries, the true value of "spacing" is .02709358.  Rounded off to .0271   (%.4f) */
      printf("\n\nSpace pickets %.4f  ", spacing); //Space pickets .0271
      //printf("\n\nSpace pickets %.8f  ", spacing);

/*  The formula for determining the measurement of the last space is:  */
            last_space = ( distance - ( (pickets * spacing) + (pickets * width) ) );
/*Here is the problem to solve.  When determining the "last_space", the true value (.02709358) of "spacing" is not the correct value to use.  The value needed now is the "rounded off" value (%.4f .0271).  How can this be done? */
           printf("\n\nLast space is %.4f  ", last_space);
      //printf("\n\nLast space is %.8f  ", last_space);
      printf("\n\nStay Open? Any key for YES, N for NO.");
      c=toupper(getch());
      if(c == 'N')
      {
      stay_open=!TRUE;
      printf("\nAdios");
      }
          }
}