Humans are amazing in their variety. A dear friend of mine would sometimes call me for help figuring out some bit of arithmetic. “Hey Nu,” she’d say, “what’s 17 percent of 200?” That’s one end of the spectrum; at the other end is this Chinese kid. Prepare to be amazed.
I am sure that it would take me over an hour to do what the kid does in two minutes. What are those weird finger movements he does while doing the additions? He’s using an imaginary abacus. They learn how to use an abacus and then practice intensively until they become so proficient that they can mentally manipulate the beads, and thus speed up their computation.
Here’s a sample of Singaporean kids doing mental arithmetic.
Bottom line: people do astonishing things provided effort and training.