title: Sass Arithmetic
body: <p>I'm trying to loop from 1 to 12 and output some span widths for an altered grid for a particular view in an app. </p>
  
  <pre><code>$span-width: 8.21875%;
  $gap: 0.125%;
  @for $i from 1 through 12 {
    $span-width: ($i * $span-width) + ($i * $gap) ;
    .span#{$i}{
      width: $span-width;     
   }
  }
  </code></pre>
  
  <p>This is outputting </p>
  
  <pre><code>.span6 {
    width: 6162%;
  }
  </code></pre>
  
  <p>How do I write the sass to calculate the widths using the usual arithmetic rules?</p>