Gu Jiu asked Xie Daji, "Don't you know how to do this? It's quite simple."
Xie Daji widened his eyes in disbelief, "Simple? Do you know how to do it?"
"Of course. It's just twenty-three, isn't it?"
Second Xie was also quite surprised that she solved it with just a glance.
"How did you figure it out so quickly?" he asked.
"Dad, Dad, did sister-in-law get it right?" Xie Erqing asked anxiously.
Second Xie ignored him and asked Gu Jiu again, "How did you work it out?"
Gu Jiu pondered for a moment. There were multiple ways to solve this type of problem, but since Xie Daji seemed rather unintelligent, she decided to demonstrate the most basic method.
"The numbers that leave a remainder of two when divided by three are three apart. Let's first list out the numbers that are multiples of three plus two..."
She wrote on the ground: five, eight, eleven...
"The numbers that leave a remainder of three when divided by five are five apart. Let's also list out the multiples of five plus three, and the multiples of seven plus two... Look at these three sets of numbers and find the one that appears in all three sets. That's the answer."
Not only Xie Daji, but even the seven-year-old Third Xie could see that the answer was "twenty-three."
Second Xie patted his son's little head and praised him with a smile, then turned to scold Xie Daji with a stern face, "Your sister-in-law is around the same age as you, but she solved it at a glance. You pondered for so long and still couldn't figure it out. Did you leave your brain at home?"
Xie Daji actually agreed wholeheartedly and nodded, "My brain hasn't been working well since I was little. I said I wanted to practice martial arts, but you all insisted I study. Since you want me to study, I'll study. But you also want me to learn math. I'm not going to be an accountant; I want to be a great general."
Second Xie scoffed, "Do you think it's that easy to become a great general? If you can't even recognize numbers, how will the soldiers you command understand your orders? If you can't do accounts, you won't even know when others embezzle military funds."
Xie Daji scratched his head sheepishly, "Oh, I see. Then I should study more?"
Second Xie glared at him.
Xie Daji smiled ingratiatingly at Gu Jiu, "Sister-in-law, could you teach me math? Uncle loves to criticize others; his words are like venom. I don't want to learn from him."
Second Xie raised the small rod in his hand as if about to strike him. Xie Daji hurriedly hid behind Gu Jiu, not at all displaying the demeanor of a future great general.
Second Xie smiled at Gu Jiu, "Ninth Sister-in-law, Brother thinks you have more patience. Why don't you teach these boys math?"
"Sure," Gu Jiu didn't refuse.
She knew that in this era, people used counting rods for calculations. Counting rods were small sticks. From one to five, they would lay out as many rods as the number. For six and above, it was somewhat like an abacus, with a horizontal rod representing five and a vertical rod underneath representing one.
Or they could lay the rods vertically to represent one and horizontally to represent five. There was no fixed rule for vertical or horizontal; it depended on personal preference.
The calculation method was actually quite similar to modern vertical notation, except that instead of simplified Arabic numerals, they used counting rods to represent each number, which was more cumbersome.
According to the original owner's memories, this era was quite backward, lacking many crops and even the abacus.
Of course, there might have been abacuses, but the original owner had limited experience and thus didn't know about them, or they were not widely used.
So she decided to introduce the abacus to this era, as a contribution from her modern reincarnation.
Gu Jiu asked Second Xie, "Brother, have you heard of the abacus?"
Second Xie shook his head, "Abacus? What's that?"
Gu Jiu still wasn't sure if abacuses existed in this era, since Second Xie was just an accountant in a remote small county and lacked knowledge, which was normal.
Gu Jiu drew the shape of an abacus on the ground with a tree branch, "The beads on the upper deck represent five, and the beads on the lower deck represent one... For counting, you do it like this..."
Second Xie was an accountant after all, so he grasped the concept immediately. He visualized the method in his mind, and his eyes lit up.
He called out loudly for Third Xie, "Third Son, Third Son, come over here!"
Third Xie put down his work and came over.
Second Xie then instructed him to make the abacus according to the drawing on the ground.
Gu Jiu carefully explained the structure of the abacus to Third Xie.
Third Xie said, "This isn't too difficult, but we currently lack the proper tools. The holes in the beads may not be smooth enough, which could affect the speed of moving the beads."
Gu Jiu was somewhat surprised. As expected of someone who often did woodwork, Third Xie immediately identified the key issue. The smoothness of the bead holes and the rods would determine the calculation speed. If either was not smooth enough, it would not be easy to slide the beads, thus affecting the calculation speed.
"It's no problem. For now, we just need to make one so we can start learning on the road. We can make better ones when we're out of the forest," Second Xie said quickly.
Third Xie had no further objections. "I'll make one after finishing Sister Gu's basket."
Gu Jiu recalled the mental abacus that was once popular in her previous life before the war broke out and decided to teach Second Xie that method as well.
For the teacher, mental abacus was just a few rhyming phrases, with the main part being the student's practice. The teacher didn't necessarily have to be able to calculate quickly, but the trained students could solve problems rapidly.
Learning this algorithm could also become a means of livelihood in the future.
Since Gu Jiu's mint and eucalyptus leaves weren't ready yet, and she had nearly depleted the nearby medicinal herbs, she had nothing else to do and contentedly became a math teacher for the day.
For someone like Second Xie who had a good foundation in calculations, Gu Jiu's explanation allowed him to grasp the tricks immediately.
He then immersed himself in the new algorithm, visualizing calculations on the drawn abacus while the children openly slacked off, which he ignored.
The people of Dahu Village were truly patient. Since the people of Huaishu Village wouldn't leave, they stubbornly refused to leave either and ended up staying in the same place.
That night, Gu Jiu still couldn't get a good night's sleep. In the middle of the night, she heard screams coming from Dahu Village again, wondering if there was another snake? The snakes really showed no mercy, even targeting the evildoers with their upright gaze.
She opened her drowsy eyes to find that Mrs. Gao had already gotten up, and the Xie brothers were all awake, looking towards Dahu Village.
When Mrs. Gao saw that Gu Jiu was awake, she patted her and gently advised, "It's nothing, go back to sleep. It's not our business."
As she finished speaking, a figure came running quickly towards them from that direction, stumbling and being chased by another person.
Xie Zhan and Fifth Xie took two steps forward to shield their family, but another figure moved even faster, shielding them from Xie Zhan and Fifth Xie.
Gu Jiu looked and saw it was Lu Aniu.
She found it odd. This Lu Aniu was rather strange, seeming to always protect the Xie family. Could the two families be related?
The running figure fell at Lu Aniu's feet, pleading in a hoarse voice, "Save me! Please, save me!"
It turned out to be a woman in her twenties, wearing tattered and dirty clothes with her collar ripped in several places and her hair in disarray, clearly terrified from some ordeal.
While everyone was surprised, the chasing person also caught up, bent over and tried to drag the woman away, "You wretched woman, come with me. Don't think the people of Huaishu Village can save you. This is a matter of Dahu Village, and they have no right to interfere!"
He forcefully pulled at the woman.
