title: undefined method `time_ago_in_words' for #<Post:0xac200b0> in Rails 3?
body: <p>I have the following code in <strong>views/posts/show.html.erb</strong>:</p>
  
  <pre><code>  &lt;span&gt;&lt;%= @post.time_ago_in_words(Time.now) %&gt;&lt;/span&gt;&lt;br /&gt;
  </code></pre>
  
  <p>And I get this error: </p>
  
  <pre><code>undefined method `time_ago_in_words' for #&lt;Post:0xac200b0&gt;
  </code></pre>
  
  <p>Any suggestions to fix this?</p>