BEIJING, CHINA—Scientists at Tsinghua University have cleaned and reassembled a collection of 2,500 thin bamboo strips dating to 305 B.C. that had once been held together with string to form 65 ancient texts. Feng Lisheng, a historian of mathematics at the university, explained that one of the texts, written all in numbers on 21 of the bamboo strips, is the world’s oldest example of a multiplication table in base 10. It may have been used to calculate the surface area of land, crop yields, and taxes. “Such an elaborate multiplication matrix is absolutely unique in Chinese history,” he said.