title: undefined local variable or method `number_to_delimited'
body: <p>I'm using rails 4.2.5.</p>
  
  <p>And in rails API (for v4.2.5.2) I see this helper:</p>
  
  <p><code>number_to_delimited(number, options = {})</code></p>
  
  <blockquote>
    <p>Formats a number with grouped thousands using delimiter (e.g., 12,324). You can customize the format in the options hash.</p>
  </blockquote>
  
  <p><a href="http://api.rubyonrails.org/classes/ActiveSupport/NumberHelper.html#method-i-number_to_delimited" rel="nofollow">http://api.rubyonrails.org/classes/ActiveSupport/NumberHelper.html#method-i-number_to_delimited</a></p>
  
  <p>But when I using this help in my views, it throws an error:</p>
  
  <p><code>undefined method</code>number_to_delimited' for #&lt;#:0x0000000b091b30>`</p>
  
  <p>Other helpers, such like <code>number_to_currency</code>， all works well. What's wrong with me?</p>