What are specific math concepts all web developers should know? [on hold]

I will start by saying that I searched the internet for about an hour and found many examples of what I would consider wide topic answers to this question. With that said, links to external resources that cover this specific topic are more than welcome.

I will frame this question in 3 parts

1. What are general math topics that are useful to web development?
2. What SPECIFIC math topics are often very recurring (occur in almost all web apps)?
3. What are some project idea’s that make learning these concepts easier to understand to someone in the early stages of web development?

Some examples (or links to) how these math topics are used in both javascript and php and how they differ between languages would be awesome as well.