cheat sheet 
noun North American informal
A piece of paper bearing written notes intended to aid one’s memory, typically one used surreptitiously in an examination.My short-term memory sucks, so I spent some time over the weekend reading up on obscure ballot measures and scribbling notes on a cheat sheet so I could just walk in, fill in the dots, then leave....
- This cheat sheet will tell you which numbers are worth crunching.
- Consider the case of a student who provides the correct answer to a test question, but who has simply copied from a cheat sheet that has been brought into the classroom.