Emily Long is a freelance writer based in Salt Lake City. After graduating from Duke University, she spent several years reporting on the federal workforce for Government Executive, a publication of ...

Once Sanaa Hiremath, 11, was home schooled, she found she could do math without writing problems down. She has a Guinness World Record, finishing a 12-digit multiplication problem in under 10 minutes.

You probably haven’t had to do longhand math in years, but you do mental math every day. Or maybe you google math problems ten times a day, because you’ve forgotten how to do any math beyond your ...