Li Yan listed the vertical form of twenty-three plus nineteen on the blackboard, and then asked the villagers in the audience, "Let's first calculate the vertical form of the units digit three and nine. Can anyone figure out what three plus nine equals?"

A quick-witted villager said, "It's twelve!"

Li Yan nodded, wrote a two on the right side of the vertical equation, and then put a dot next to it. "Since it's twelve, let's write the two first, and use this little dot to record the remaining ten. We'll deal with it later!"

"Then let's look at the tens place in vertical form. What is twenty plus ten?"

This one was easy, the villagers blurted out, "Thirty!"

Li Yan nodded. "Since it's thirty, and the little dot we just recorded is also ten, then the total is forty. Li Yan wrote another four, so this number represents forty-two!"

Some smart people have already reacted, but most are still confused. How can the number be forty-two just like that?

Li Yan demonstrated the convenience of vertical calculations and introduced the simple application of Arabic numerals, which aroused their strong interest. Then she said to the villagers, "Okay, today's class will start with familiarizing ourselves with the numbers from zero to one hundred."

Li Yan quickly listed the numbers from zero to one hundred on the blackboard. "Today, uncles, your task is to memorize all these numbers. Not only must you memorize them, but you must also write them down from memory! Once you're familiar with these numbers, simple addition and subtraction problems won't be difficult for you!"

The villagers were very excited. They actually discovered that except for the numbers from zero to nine, which needed to be remembered, the other numbers could be combined according to patterns and did not require special memorization.

The villagers found that using this vertical method, adding two numbers and counting seemed not so difficult. They just needed to remember what to calculate first and what to calculate next, and the final number was the result.

Unlike counting rods which require tools, this arithmetic method only requires a vertical formula. After a simple addition of the units digits, the result will be clear at a glance.

After becoming familiar with the numbers and calculation rules, the second half of the class was spent on practice. Li Yan wrote questions on the blackboard and asked the students to answer them. The villagers were unfamiliar at the beginning, but gradually became able to answer them, and their confidence emerged unconsciously.

Li Yan smiled and said, "Look, uncles, this arithmetic isn't difficult, right? That's all for today's lesson. Go back and practice more. We'll learn subtraction tomorrow!"

"What? You're going back now? We're studying hard!" some villagers said.

"Right, right, right. Girl, give us a few more questions!"

The villagers' enthusiasm is now at an unprecedented high. They originally thought that arithmetic was something very profound and mysterious, but today they see that it is nothing more than that!

They can learn too!

"Too much is too little. Uncles, you should first firmly grasp what you learned today. This is the foundation. Only by mastering the basics can you achieve twice the result with half the effort in future studies!"

At this time, Zheng Hui, who was sitting at the bottom, had already stared into her eyes. This counting method was so simple that even she, who didn't like arithmetic, could listen to it with great interest.

On the other side, Lu Kang, who was standing outside the door and watching, was also greatly shocked. If one remembered this method, some simple numbers could actually be quickly calculated by mental calculation.

He was moved slightly and imitated this method, trying to add three-digit numbers in his mind. In a moment, he got the result and couldn't help but exclaimed, this method is wonderful!

It was getting late, so Li Yan took Zheng Hui back first. The villagers were still reluctant to leave after Li Yan left. They stood in front of the blackboard in groups of three or four, giving each other questions to test them.

At this moment, they felt that they had mastered the secrets of arithmetic. They were so excited that they stayed in the dormitory and refused to leave.

While eating, Zheng Hui kept looking at Li Yan with starry eyes.

Li Yan felt a little uncomfortable with Zheng Hui's embarrassed gaze, "Why are you looking at me like that? Eat!" After saying that, she picked up a piece of food for Zheng Hui with chopsticks.

"I can't come tomorrow, so please explain the subtraction to me later!" Although she wanted to ask her why she knew so much strange knowledge, she also knew when to advance and retreat. Instead of getting an evasive answer, it would be better to ask about the things that interested her.

Li Yan nodded.

After dinner, Li Yan talked to Zheng Hui about subtraction operations. Zheng Hui already had a basic understanding of it, so Li Yan only briefly explained the rules, and she was able to fully understand and grasp the mysteries.

When the sun wasn't so scorching, Zheng Hui stood up and said goodbye. "It's getting late, I'll go back now. Thank you so much for sharing so much interesting information with me today!"

Before leaving, Li Yan took a small handwriting blackboard and chalk from the utility room, and then sent Zheng Hui away.

After sending Zheng Hui away, Li Yan went to the backyard.

Yesterday she pressed the copied paper on the wooden table to remove the moisture, and it should be almost done by now.

Li Yan moved the heavy object covering the paper away and began to peel off the paper carefully.

She tried many times, but the papers were always stuck together. She finally peeled off one, but when she was halfway through, the paper was torn.

Li Yan was originally quite excited, but suddenly became depressed. She had failed many times. What went wrong?

Li Yan recalled the steps of papermaking in her mind: soaking, boiling with lime, washing, picking out impurities, repeatedly beating, chopping, and finally putting into pool water to make paper. She had done all these steps herself, so why did she always fail?

Li Yan looked at the pile of paper again. Since the paper could be made, there should be no problem with the steps. Now the papers were easy to stick together and difficult to separate. There must be a key step missing.

After analyzing this possibility, Li Yan paced back and forth anxiously, wondering which step she had missed.

Suddenly she stopped, her eyes shining, she thought of something, it was paper medicine. If she wanted the paper she copied to be less likely to stick together after it was formed, she needed paper medicine!

How could she forget such an important thing!

She remembered that adding paper medicine could greatly improve the paper's curtaining properties, making it easier to peel off after pressing!

She recalled that the walnut vine could be used, but then ruled it out, saying it wasn't available here.

It seems that peach branches or grape vines would also be possible.

In fact, the so-called paper medicine is the liquid made by mashing and boiling the roots, stems and leaves of some plants. This liquid can easily improve plant fibers in the papermaking process and facilitate the formation and separation of paper!

It was because she was missing one step that she never succeeded!

Thinking of the key to papermaking, Li Yan was very excited and immediately found her grandfather to help her find some vines and branches.

This thing was not difficult to find, so Mr. Li agreed immediately.

After talking to her grandfather, Li Yan ran back to the backyard and started preparing again with high morale.