title: Generate a Random Output from the List of Multiplicities of a Number X up to a MAX Number Y?
body: <p>Using a bash script, I want to choose a random number from such a list: [0, X, 2X, 3X, 4X, ..., Y] where Y=k*X and k is an integer. X and Y are just some input numbers by the user. To clarify the question, here is an example:</p>
  <pre><code>X=2
  #Y=10*X
  Y=20
  # The &lt;desired_command&gt; to choose a random number from [0, 2, 4, 6, 8, ..., 20] --&gt; sample output=12
  desired_command
  </code></pre>
  <p>How can I do this?</p>