Marianne, I cannot answer your question regarding the versions of Excel definitively when two versions are installed on the same machine. Generally, as far as Windows is concerned, I would expect that the "Excel choice" it presents in the short list will either be the newest version (more likely) or the one that has been installed on the machine most recently (possible).
Your best bet is to find the precise folder on your machine where Excel 2010 is installed and make a note of that before going into Default Programs. You are presented with a Browse option (before Win10) or "Choose a different app" (or something similar in Win10) that allows you to navigate to the folder where the program you want to use resides and to select that as the default. It's been a long time since I last needed to do this, but have been in a couple of situations similar to yours where using an older version of a given program was preferable to the newer one, and I had to follow the previously mentioned steps then browse for the program I actually wanted to use. Brian
