I'm at the end of my rope here. I'm trying to install QGIS 3.2 on my computer running Linux Mint 18.3 and I've gone through installing the unstable PPA and updating and upgrading half a dozen times and it just installs 2.18. I'm supposed to be using 3.2 for a class, and I don't understand why I'm getting 2.18 when I am not using the LTR PPAs. If someone could give me an idiot-level explanation of how to get 3.2 installed (and more important WHAT I am doing wrong), it would be a lifesaver.
Adding the QGIS ubuntugis xenial main repository did the trick. The note on the supported distribution chart says: "5] 3.0 and above only available with ubuntugis-unstable (plain xenial lacks GDAL2)" so I assumed that was the only repository I needed.