title: Calculate percentage increase using math formula
body: <p>I have a function that calculates percentage increase of 2 numbers:</p>
  
  <pre><code>const 1st_num = 50
  const 2nd_num = 100
  
  percentage = ((1st_num - 2nd_num) / 1st_num) * 100  // -100
  </code></pre>
  
  <p>It seems correct but what if the 1st number is 1?</p>
  
  <pre><code>((1 - 50) / 1) * 100 // -4900
  </code></pre>
  
  <p>I don't see it making sense anymore. What am I missing?</p>