Resposta :
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int main()
{
srand(time(NULL));
int vetor[100], i, div_3 = 0;
for (i = 0; i < 100; i++)
{
vetor[i] = rand()%51;
printf("%d\t", vetor[i]);
if (vetor[i] % 3 == 0) div_3++;
}
printf("\nDivisiveis por 3: %d\n", div_3);
return 0;
}