how to change a src of image by number?

how to change a src of image by number?

Hi all,

I have this:
     
<div id="holder">
      <img src="/website/path_off.gif" class="test">
      <img src="/website/path_off.gif"  class="test">
      <img src="/website/path_off.gif" class="test">
      <img src="/website/path_off.gif" class="test">
</div>

how, I have another js function:

function activeit(number)
{
       // here    
}

in here I need to change the image by the number:
for example:
      The number is 1 then:
            1. ALL images are: <img src="/website/path_off.gif" class="test">
            2. the FIRST image change to :   <img src="/website/path_on.gif" class="test">
      and so on..

how to do it using jquery please?
thanks for help!