title: Insert a number to the random position in an array of random number
body: <p>I'm developing a simple game to add 2 number and select a result in a gridview. But I've only put a number to 1st or last position of my list's Array. How to add my result to the random position without give it an exactly index? 
  Here is my code:</p>
  
  <pre><code>x=random.nextInt(11);
  a=a+x;
  for (int j=1;j&lt;25;){
      int random=((int)(Math.random()*25))+1;
      if (!list.contains(random)){
          list.add (a+random);
          j++;
      }
  }
  </code></pre>