Is there an app avilable on the iPad which allows me to edit Excel spreadsheets and use formulas?

There's apple's Numbers, I use Documents to Go, and I'm sure there are others.

I know they'll allow you to read excel and probably do some minor editing, but I'm not sure how much forumla stull you'll be able to do. All word processing apps are skinnied down versions of their originals, usually with limited functionality. (for example with word I can change fonts, but to a limited variety, do bolding and italics and tabbing but fancy tables won't happen)

Microsoft has no interest in releasing office for ios.

So you will have to use something else with limited compatibility.

Look in the app store, there are a ton of productivity apps.

Apple's iWork apps

http://www.apple.com/iwork/

3rd party Microsoft equivalent apps

http://www.polarisoffice.com/en/iOS.asp

http://itunes.apple.com/sg/app/quickoffice-pro-hd-edit-office/id376212724?mt=8&l s=1

http://itunes.apple.com/sg/app/office2-hd/id364361728?mt=8&ls=1

http://itunes.apple.com/sg/app/documents-to-go-premium-office/id317107309?mt=8&l s=1

http://itunes.apple.com/sg/app/polaris-office/id513188658?mt=8&ls=1

Others, including cloud based

• Microsoft Office Web Apps:These are versatile apps since they can be used on or off the cloud. Expect a simplified experience to the full version of Microsoft Office suite.
• OnLive: Access both a degree of Windows desktop functionality and full Windows versions of Microsoft Office Suite.
• CloudOn: This was one of the first solutions for iOS productivity. Syncing with Dropbox, CloudOn offers a more complete Windows desktop. The tradeoff is it also offers a more pared-down version of Word, Excel, and PowerPoint.
• rollApp: Offers Open Office programs for iOS, also utilizing Dropbox.
• LogMeIn: Remotely access your home computer's desktop from your iOS device. This solution requires coordination of logins, settings, and hookups. The free version does not offer file transfer, but you can get a separate, free app for that.
• Google Docs: Now featuring Google Drive for iOS, users no longer have to battle with pressing the Refresh periodically to initiate syncing. This makes collaboration much smoother, resulting in a stronger office productivity product.