Excel for Mac 2011 now includes the Solver add-in built-in. You do not need to install and run the 3rd Party Solver add-in.
Before You Begin
Before you are able to install the Solver add-in for Excel for Mac 2011, you are required to install Microsoft Office for Mac 2011 Service Pack 1 (14.1.0). Open an Office for Mac 2011 application, go to Help --> Check for Updates and install the 14.1.0 update.
Install Solver Add-in for Excel for Mac 2011
Open Excel for Mac 2011
Go to the Tools menu, select "Add-ins"
Check "Solver.Xlam" then click OK
After restarting Excel for Mac 2011 (fully Quit Excel 2011), select the "Data" tab, then select "Solver"