title: Math function to find the biggest multiple of a number within a range
body: <p>I want to know if there is a math expression that I can use to find this relation between two numbers.</p>
  
  <p>Some examples of the input and expected output are below:</p>
  
  <pre><code>Input    Multiple   Result
  4        3          3
  6        3          6
  8        3          6
  4        4          4
  12       4          12
  16       5          15
  </code></pre>
  
  <p>Also, the expressions below from Wolfram Alpha show me the expected result but since they don't expand on the explanation on how to do it I can't learn from them...</p>
  
  <p><a href="http://www.wolframalpha.com/input/?i=biggest%20multiple%20of%204%20from%2010" rel="nofollow noreferrer">Biggest multiple of 4 from 10</a></p>
  
  <p><a href="http://www.wolframalpha.com/input/?i=biggest%20multiple%20of%204%20from%2012" rel="nofollow noreferrer">Biggest multiple of 4 from 12</a></p>