The first time I did it, I got a message box saying something to the effect it could not open and asking me to send report to Apple and I clicked send. Now, nothing happens when I click on the link. The site is http://www.moneysense.ca/ror/ and the formulas in the spreadsheet are designed to produce return on investment using uneven the dates of deposits and withdrawals in an investment account - the interesting part is it uses the actual dates which are inserted and are not regular to perform its calculations.
This note, from a cell in the Excel spreadsheet, likely explains the difficulty:
If you are using on older version of Excel, you may need to install an “Add-In.” On the Tools menu at the top of your screen, click Add-Ins. Select the Analysis ToolPak box, and then click OK. If necessary, follow the instructions in the setup program.
The add-ons in Excel's Analysis Toolpak are, to the best of my knowledge, not supported in Numbers.