Hopefuls sat in extreme heat and cold, did math in 145-decibel rooms (normal conversation is 60 dB), and spent hours in isolation chambers. On top of all that, candidates took 12 intelligence tests. These exams sought to predict a wealth of unknowns: how the men would maneuver spacecraft, if they could problem-solve midflight, and whether they grasped the science that would keep them aloft. What follows is a subset of those brain teasers for you to try. May John Glenn be with you.