The Tianyuan Abacus: Interest on Interest

Amuer Qiqige, a Mongolian girl who studies under the master astronomer and calendar mathematician Guo Shoujing, carries the healing wisdom of her family's Miao heritage and a deep desire to help others. When the Persian merchant Nasir Ding uses a “compound interest” formula to fleece the merchants of Dadu, she quickly sees the “exponential poison” devouring their wealth. From a nighttime showdown with counting rods to policy debates at the khan's court, Amuer wields the tianyuan method as her blade, devising fair lending formulas and outsmarting the Semu merchant caravans. Rather than fight violence with violence, she builds on mathematics, combining the Miao understanding of “balance” with medicine's pursuit of “dispelling evil and restoring the good.” She helps bring about the Fair Commercial Tax Regulations, making mathematical wisdom a remedy for preserving order in trade. Amid the bustle of Yuan-era Dadu, she writes a legend of using mathematics to serve the people. See how this brilliant young mathematician clears the fog with her counting rods and measures fairness with formulas!