var strRotate='';

var y = Math.round(11*Math.random());
switch(y)
{
case 0:
  strRotate="tiermidcol_customer_a";
  break;    
case 1:
  strRotate="tiermidcol_customer_b";
  break;   
case 2:
  strRotate="tiermidcol_customer_c";
  break;
case 3:
  strRotate="tiermidcol_customer_d";
  break;   
case 4:
  strRotate="tiermidcol_customer_e";
  break;   
case 5:
  strRotate="tiermidcol_customer_f";
  break; 
case 6:
  strRotate="tiermidcol_customer_g";
  break; 
case 7:
  strRotate="tiermidcol_customer_h";
  break; 
case 8:
  strRotate="tiermidcol_customer_i";
  break;
case 9:
  strRotate="tiermidcol_customer_j";
 break; 
case 10:
 strRotate="tiermidcol_customer_k";
 break;  

default:
  strRotate="tiermidcol_customer_a";
  break;  
} 

var strImages='';
strImages+='<div class="'+strRotate+'">';
document.write(strImages);