For anyone looking for a good use for their $5, here's a suggestion. All of the Very Short Introduction To series from Oxford U. Press are $6.15. Covers a very wide range of subjects. Here's the link, though I don't think it captures quite everything. I found something through looking through the available titles listed at the front of one of the sample pages Amazon shows; it was available on Google when I looked it up, but I don't believe it showed on this list.
https://play.google.com/store/search...uction&c=books