How does my dual core i5 in my MacBook Pro have more than 400% CPU usage? [duplicate]

If you look here, you have 2 cores that can execute 2 threads each with turbo boost. So I would assume 400% is your maximum. Seems likely that Adobe maxed out one CPU completely, and the other CPU was running the OS and other tasks.

The additional usage may be because your 2.7 ghz CPU was turbo boosted to 3.1 ghz at the time.

Also, within Activity Monitor, you can choose Window -> CPU History, and it will break down everything. For example on my 6 core Xeon, I have 12 graphs.

This system also supports "Turbo Boost 2.0" -- which "automatically increases the speed of the active cores" to improve performance when needed (up to 3.1 GHz for this model) -- and "Hyper Threading" -- which allows the system to recognize four total "cores" or "threads" (two real and two virtual).

(as found on this page)

The turbo boost lets your processor go beyond the 100% threshold for intensive tasks