Numbers Excel Compatibility

Read Only - Compatibility Mode - Excel - Microsoft Community
Is Numbers Compatible With Excel? - Apple Community

I found Numbers to be very poor in terms of compatibility with Excel, have you thought about Office 365? As for Numbers to Excel, that should be better because you're using teh lowest common denominator, i.e., going to less features (numbers) to more features (Excel) so it should export. In Excel, there are several ways to combine text and numbers. Use a number format to display text before or after a number in a cell If a column that you want to sort contains both numbers and text—such as Product #15, Product #100, Product #200—it may not sort as you expect. This behavior is based on a supposition that the application that last saved this file does not have the full feature set of Excel (a correct supposition in this case) and that in order to maintain compatibility with the other application, a reduced feature set is imposed (a faulty supposition in this case).

There have been a number of posts regarding compatibility of excel files in numbers/iPad. I recall one user saying that there are frequent times when an excel sheet doesn't translate well - so that tells me compatibility may be iffy, perhaps dependent on advanced features used in the excel file. If I recall correctly, some users have found problems opening numbers/mac files on iPad.
I have pretty much vanilla looking excel files (data and formulas) that translate well in numbers/iPad. So YMMV.

Read Only - Compatibility Mode - Excel - Microsoft Community

Is Numbers Compatible With Excel? - Apple Community

Mar 10, 2011 8:15 AM