These Indian kids don’t need a calculator to solve mathematical operations in just seconds. They do it all in their heads using a mental abacus—an old Asian technique that allows them to visualize an imaginary abacus and operate it to perform the calculations.
https://www.youtube.com/watch?v=3wgdkFwvrEQ
This video explains how it works—just don’t pay attention to the exaggerated marketing statements:
