Math Brain Teasers

https://www.eduplace.com/kids/mw/bt/bt_5.html

https://www.eduplace.com/kids/mhm/brain/gr5/

http://www.learn-with-math-games.com/math-brain-teasers.html

http://www.cashmancuneo.net/math_puzzles/files/35mathpuzz.pdf