John Carlos BaezThe students built base-20 abacuses. These were initially intended to help convert decimal numbers to base 20 and vice versa, but soon the students started using them to do arithmetic in base 20.
The upper section of their abacus has 3 beads in each column for the values of the sub-base of 5, while the lower section has 4 beads in each column for the remaining units.
(2/n)
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