Revision 70e352e6-f730-4ade-b284-98fbf37b8d70 - Software Quality Assurance & Testing Stack Exchange

You can make use of storeEval command in Selenium IDE. Using it you can add, divide, multiply any variable with desired value and then use it.

Command: storeEval
Target: storedVars['delay']*2
Value: doubleDelay

    <body>
    <table cellpadding="1" cellspacing="1" border="1">
    <thead>
    <tr><td rowspan="1" colspan="3">New Test</td></tr>
    </thead><tbody>
    <tr>
    	<td>store</td>
    	<td>5000</td>
    	<td>delay</td>
    </tr>
    <tr>
    	<td>storeEval</td>
    	<td>storedVars['delay']*2</td>
    	<td>doubleDelay</td>
    </tr>
    <tr>
    	<td>echo</td>
    	<td>${doubleDelay}</td>
    	<td></td>
    </tr>
    
    </tbody></table>
    </body>

[reference for storeEval][1]


  [1]: http://www.questionselenium.com/2012/10/echo-storeeval-and-storedvars.html