There is the practice of anzan in China and Japan, which shifts the burden of calculation into the visual cortex by visualizing a mental abacus. Thus advanced

There is the practice of anzan in China and Japan, which shifts the burden of calculation into the visual cortex by visualizing a mental abacus. Thus advanced practitioners can rapidly and correctly evaluate calculations like the one you have given. As you can see, Tsujikubo's speed in divisions appears to be limited in her ability to physically write out the answer. https://youtu.be/-9T3P--ubQc?t=6m10s https://youtu.be/-9T3P--ubQc?t=6m10s Granted, these are people at the top of their game, so may not qualify as "normal" per your argument, but this is to illustrate that the limits of numerical calculation in "normal" people may be the algorithms we are taught rather than the computational capacity of our brains.