The bat-and-ball problem is a famous math puzzle that more than half of people—even Harvard graduates—get wrong. It's ...

The puzzle reads: 3 + 4 = 19 5 + 6 = 4 1 2 + 8 = 66 5 + 1 = ? At first glance, none of these make sense. According to standard math, 3 plus 4 is 7 — so how do we ...