I think keeping it simple is great, but you should bring your terminology in the text to be consistent with the diagram at the start, otherwise it's confusing.

I don't think it would be difficult to say something like:

> P and NP are two different kinds of problems. P problems are easy for computers to solve, and NP problems are easy for computers to check answers for. All P problems are NP problems; that is, if it's easy for the computer to solve, it's easy to verify the solution. The P vs NP problem asks: within the class of NP problems, are there problems which are not P, that is, which are not easy for computers to solve?