title: Best way to write this calculation in Ruby?
body: <p>What is the best way to write this calculation in Ruby?</p>
  
  <pre><code>amt = self.alt_inv - (self.alt_tax ? self.alt_tax : 0)
      - (self.alt_freight ? self.alt_freight : 0)
      - (self.misc1_amt ? self.misc1_amt : 0)
      - (self.misc2_amt ? self.misc2_amt : 0)
  </code></pre>