title: Add to value based on radio button value
body: <p>This is hard to describe so I'll try my best. </p>
  
  <p>I have a script working fine, based on the radio button selected, it prints the value to a text box that is disabled for editing. I have to take this one step further...I need that value to then be involved in an addition function, adding the value of the radio button. </p>
  
  <p>This is what I tried and it failed. No errors but doesn't add what I want it to. If I remove the if statements, it works but only prints the initial value of the radio button. I need to add to that value based on what is selected. </p>
  
  <p>edit: adding html as requested. </p>
  
  <pre><code>&lt;center&gt;
  Choice1 : &lt;input type="radio" name="region" id="choice1" value="10.25"&gt;
  Choice2 : &lt;input type="radio" name="region" id="choice2" value="11.25"&gt;
  Choice3 : &lt;input type="radio" name="region" id="choice3" value="8.25"&gt;
  &lt;/center&gt;
  
  //Enter how many in this box
  How many?  &lt;input type="text" id="addtl" size="3" maxlength="2"&gt;&lt;/input&gt; @ 
  
  //this is the choice, based on radio button, add something to it
  &lt;input type="text" id="add_cost" size="2" maxlength="6"&gt;&lt;/input&gt;
  
  &lt;script&gt;
  //print in the box 
  
  $('input[name="region"]').change(function(){
  $('#add_cost').val($('input[name="region"]:checked').val());
  if(add_cost == 11.25)  {
    add_cost + 4;
  }
  else if (add_cost == 10.25){
    add_cost + 1;
  }
  else if(add_cost == 8.25){
    add_cost + 3;
  }
  
  });
  
  
  
  &lt;/script&gt;
  </code></pre>