Chapter 28: Arithmetic (Part One)

  Xun You heard Cao Zhi was looking at the records of grain and fodder, and he was shocked. He hastily went forward. Although Cao Zhi appeared intelligent and mature in front of everyone, after all, he was still a child. Xun You feared that he would ruin the records of the number of grain and fodder.

  Just as he was about to go forward, he was stunned for a moment. But seeing that the number he had not yet calculated on the book had already been filled in by someone, Xun Yu furrowed his brow and stared at Cao Zhi.

  Feeling Xun Yu's gaze, Cao Zhi scratched his head and said: "Master Gongda, I was idle just now and saw that there were some places that hadn't been done yet, so I took the liberty of completing them for you. If there are any mistakes, please don't blame me."

  Xun You hummed softly, snatched the book, and then picked up the abacus on the desk to start calculating as if no one was around. Cao Zhi could only helplessly rub his nose and step aside. Guo Jia came forward, pulled Cao Zhi over, and whispered in a low voice: "Fourth Master, you should know that what Gong Da dislikes most is someone messing up what he's doing."

  Cao Zhi put on an innocent look and said, "I just wanted to help Mr. Gong Da reduce his burden."

  Mao Jing also shook his head and said, "Fourth Master, you are kind-hearted, but the arithmetic is extremely complicated. If you make a mistake, there will be a huge deviation in the allocation of food and grass for the entire army. If the general finds out, he will surely punish us severely."

  Seeing Guo Jia and Mao Jie's serious faces, Cao Zhi shrugged his shoulders and said, "Actually, it's not that difficult..."

  Guo Jia heard this and his eyes lit up. Since he had come into contact with Cao Zhi, he felt that this fourth son was not simple. At this time, he asked: "Fourth son, have you studied arithmetic?"

  "Hmm... learned a bit, I suppose." Cao Zhi also didn't know how to answer Guo Jia's question and just gave a vague response.

  Liu Ye didn't intend to let him off so easily, and softly recited: "Fourth Master has studied arithmetic, so he should know that one step is half a tian. To ask for one mu of land, from which geometry?"

  Liu Ye's question is one of the more famous questions in the "Nine Chapters on the Mathematical Art", which was written in the middle of the Eastern Han Dynasty. At that time, each large family had several copies of this book. In addition to letting their children learn arithmetic, they would also let the housekeeper learn it to help with counting.

  Cao Zhi had been in the Eastern Han for so long, but he had never studied the "Nine Chapters on Arithmetic". However, this simple question was not difficult for him. After a moment's thought, he smiled and replied: "One hundred and sixty steps."

  "Huh? So quickly calculated?" Liu Ye was secretly surprised in his heart, thinking that Cao Zhi had read the "Nine Chapters on Arithmetic" and seen this problem before. After a moment's thought, he asked: "Tian Guang six steps. If Tian has eight and a half mu of land, how many from which direction?"

  Cao Zhi slightly furrowed his brow and thought to himself, "This Liu Zi Yang really doesn't give up." Actually, the question Liu Ye asked wasn't difficult, he had just changed some of the numbers from before. However, between bu and mu, there was still a difference of one unit, chi. Because one bu is equal to five chi, and one mu is six thousand square chi, as long as you convert the units properly, even a primary school student on the street eighteen hundred years later would know how to calculate it.

  Just now Liu Ye's first question was relatively simple in numbers, Cao Zhi could still calculate mentally, but this question had to be calculated with a pen. But even with a pen, it wouldn't be difficult for Cao Zhi.

  He took a cup of water from the side table, and Cao Zhi dipped his finger in it and began to write on the table. Guo Jia, Liu Ye, and Mao Jie were curious, and they all gathered around to watch. However, when they saw that Cao Zhi had written a large number of symbols on the table that they had never seen before, they were all amazed, but they did not dare to disturb Cao Zhi's thoughts.

  In less than half a stick of incense time, Cao Zhi had already lifted his head and smiled: "Three hundred and forty steps."

  "What? So soon?" Liu Ye and the other two were extremely surprised, but Mao Jie was somewhat skeptical, and like Cao Zhi, he dipped his brush in water to calculate.

  Cao Zhi also looked at Mao Jie with great interest, wanting to know how people in this era calculated. However, the people of this era used Chinese characters as a calculation tool, and recording was quite troublesome. Mao Jie calculated on the desk for a while, but it didn't work out. He then went to Xun Yu's side, took a few counting rods, and with the help of the counting rods, spent more than an incense stick's worth of time before finally calculating the answer. Only after getting the answer did Mao Jie exclaim in surprise: "Three hundred and forty steps?"

  Guo Jia and Liu Ye were shocked when they heard this, thinking that Cao Zhi was just making a random guess. But unexpectedly, his answer was exactly the same as Mao Jie's. It should be known that Mao Jie had been in charge of managing grain and fodder for a long time, and his arithmetic skills were among the best among the people. Even compared to Xun Yu, who was constantly facing his books, he was not inferior in any way. However, even Mao Jie, an expert in arithmetic, still needed the help of counting rods and spent more than a quarter of an hour before he could calculate the answer. Cao Zhi's calculation method and speed were truly top-notch.

  But everyone's surprise did not stop there. Xun Yu, who was originally silently calculating on the other side, suddenly exclaimed: "The numbers calculated are actually all correct?"

  As soon as Xun Yu spoke, everyone in the tent looked at Cao Zhi with surprised eyes, making Cao Zhi's face turn red. He rubbed his nose and said, "Gentlemen, why are you looking at me like that?"

  Guo Jia reacted the fastest, and immediately thought of the symbols Cao Zhi had just written on the desk. He hastily approached the desk to take a look. However, what made him disappointed was that the water on the desk had already dried up, and those symbols were gone without a trace. Nevertheless, this did not dispel Guo Jia's suspicion. With a faint smile, he stared at Cao Zhi and said, "Fourth Master, why don't you come with me to explain your calculation method?"

  Cao Zhi saw it, and in his heart he secretly thought: "Indeed, I couldn't deceive this genius." However, the main purpose of his visit was to change the outdated counting method of this era. So, he didn't hide it either, but instead smiled and said: "Actually, my arithmetic level may not be as good as that of the gentlemen present, but I just used a more convenient counting method."

  A more convenient way of counting, upon hearing Cao Zhi's words, Mao Jie immediately thought of the symbols that Cao Zhi had just written, and at the same time glanced at the abacus in front of him. The so-called abacus is actually a kind of counting tool used in ancient China, which has been used for a long time, from the Han Dynasty to the Ming and Qing Dynasties. However, the abacus belongs to high-end goods, and others can only use the method of tying knots to record numbers.

  At this time, Xun Yu also couldn't help but show his curiosity and surrounded him. Cao Zhi was not afraid, and he had someone bring in a tree branch from outside, then on a relatively soft patch of mud inside the tent, using the branch as a pen, he wrote out the ten extremely common Arabic numerals 0 to 9. Only afterwards did he say to the crowd: "Zhi uses these symbols to replace Chinese characters for calculations, this is zero, this is one..."

  When they saw the new symbol, everyone didn't show a surprised look, but instead became more puzzled. This was just changing Chinese characters around, and in fact it wouldn't have much impact on arithmetic. But Cao Zhi took another step forward, which made the four people see that there were several points of astonishment afterwards.

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