no-brainer

noun2

1. •
   (informal) An easy or obvious conclusion, decision, solution; something requiring little or no thought.

   • Choosing the older version which was as good as the newer version for half the cost was a no-brainer.
2. •
   (informal) A conundrum requiring little or no thought to solve; A problem with an easy or obvious conclusion, decision, solution.

   • This next exam question is a no-brainer.