// jar I has 10 green jelly beans, 5 purple; jar II has 4 and 4;  pick 1
// at random from I, put in II, pick 1 at random from II; find
// P(bean from II was originally in I | bean from II is purple);
// should be 1/13

#include <stdlib.h>

int nreps,purplecount,wpcount;

main(int argc, char **argv)

{  int i,bean1,bean2,wasin1,purple2; 

   nreps = atoi(argv[1]);

   for (i = 0; i < nreps; i++)  {
      bean1 = 15 * (float) drand48();
      bean2 = 9 * (float) drand48();
      wasin1 = (bean2 == 0);
      purple2 = (bean1 <=4 && bean2 <= 4) || 
                (bean1 > 4 && bean2 >= 1 && bean2 <= 4);
      if (purple2) {
         purplecount++;
         if (wasin1) wpcount++;
      }
   }

   printf("%f\n",((float) wpcount/purplecount));

}