Duke of Zhenguan

The first month of the lunar calendar passed quietly.

As the Awakening of Insects approaches, although Chang'an in February is still cold, the weeping willows along the river have already begun to quietly sprout buds.

Lin's Noodle Shop remains very busy every morning.

The number of guests gradually decreased as the sun rose high in the sky.

By noon, the shop was finally empty of customers. Lin Chuan leaned over the counter and wrote on a piece of paper with a pen and paper:

Xiaoming has a water tank. It takes eight hours to fill the tank when only pipe A is turned on. It takes six hours to fill the tank when both pipes A and B are turned on at the same time. If pipe B is changed to a drain pipe and both pipes are turned on at the same time, how long will it take to fill the tank completely?

After finishing writing the question, Lin Chuan smiled mischievously, then put down his pen and waited for Yan Xiangshi to arrive.

After waiting for about half an hour, Yan Xiangshi arrived as promised, but with a girl dressed as a man behind him.

The girl was about thirteen or fourteen years old, tall and slender, with a small oval face and phoenix eyes. Although she was still young and her eyes and brows still had a childlike quality, her gentle temperament was hard to hide even when she was dressed in men's clothing.

Lin Chuan glanced at him, then bowed respectfully to Yan Xiangshi.

"Master Yan!"

"Lin Dalang, this is my granddaughter, the sixth in her family!"

"Sixth Brother, this is Lin Chuan!" Yan Xiangshi nodded and introduced the girl behind him to Lin Chuan.

Yan Liuniang blushed and curtsied to Lin Chuan:

"Greetings, Young Master Lin!"

"Greetings, Lady Yan Liu!"

Lin Chuan politely cupped his hands in greeting to Yan Liu Niangzi and invited the two to sit down:

"Master Yan, Madam Yan, please have a seat. I'll go make some tea!"

The tea was purchased a few days ago; it's tea powder made by drying tea leaves and then grinding them into powder.

Lin Chuan searched all over the West Market and even went to the East Market, but he still couldn't buy the green or black tea he wanted.

Thus, Lin Chuan had no choice but to follow local customs and make milk tea for Yan Xiangshi and Yan Liu Niangzi.

After Lin Chuan brought out two cups of tea, Yan Xiangshi took out a piece of paper from his pocket and handed it to Lin Chuan, saying smugly:

"I really couldn't solve the problem I brought back yesterday, but Xiao Liu is quite talented in mathematics. She solved it, even though I couldn't!"

Xiao Liu not only solved it, but also set a problem for you. See if you can solve it?

Lin Chuan chuckled. Ever since Yan Xiangshi discovered Lin Chuan's impressive mathematical skills a few days ago, he had been competing with Lin Chuan.

The questions became increasingly difficult. At first, they were only at the level of fifth or sixth graders, but later they were almost at the level of first or second graders in junior high school.

For Lin Chuan, this level of difficulty was naturally not difficult.

But being tested by Yan Xiangshi every day, Lin Chuan also developed a mischievous sense of humor and started giving Yan Xiangshi questions in return.

The difficulty level is kept at the level of the second or third year of junior high school.

Yesterday, he gave Yan Xiangshi a challenge: two carriages traveling towards each other. It was indeed quite difficult. His intention was to make Yan Xiangshi back down, but unexpectedly, Yan Xiangshi, lacking martial ethics, actually found a helper.

When he took the paper from Yan Xiangshi, he found that the question was still the same one he had come up with about two carriages, only the question of "moving towards each other" had been changed to "moving in the same direction".

After reading the question, Lin Chuan provided the answer:

"The two places are sixty-four li apart, is that correct?"

Yan Xiangshi was stunned for a moment, then subconsciously turned his gaze to his granddaughter.

Yan Liu Niangzi's beautiful phoenix eyes widened as she stared intently at Lin Chuan.

Seeing his granddaughter's expression, Yan Xiangshi knew that Lin Chuan must have answered correctly.

He never thought his granddaughter could stump Lin Chuan, but this speed was just too fast!

Looking at the two of them, Lin Chuan wasn't very happy. Modern mathematics had long since developed into a complete and enormous system. Although he only scored around 120 points on the college entrance exam, comparing himself to someone from the Tang Dynasty still felt like a dimensional reduction attack.

Having achieved his goal, he was no longer willing to play with Yan Xiangshi. He went to the counter, retrieved the newly created question, handed it to Yan Xiangshi, and said with a smile:

"Master Yan, would you like to take a look at this question?"

Yan Xiangshi took the paper, glanced at it, and then handed it to his granddaughter.

After watching for a while, Yan Liuniang shook her head at Yan Xiangshi with a bitter face.

Yan Xiangshi took the paper his granddaughter handed him back, and asked Lin Chuan with a wry smile:

"Kid, how exactly did you learn math?"

"Master Yan, didn't I tell you? When I was young, I learned some things from a wandering Taoist priest!" Lin Chuan said with a smile.

"A wandering Taoist priest? Boy, I'm not bragging, but even the mathematics teacher at the Imperial Academy is probably not as good as Xiao Liu in mathematics, much less as good as you! How could a wandering Taoist priest teach a student like you?" Yan Xiangshi said irritably.

"Master Yan, perhaps I have a talent for mathematics?" Lin Chuan said with a smile.

"Perhaps..."

Yan Xiangshi nodded with a wry smile, picked up the paper, and said with a look of disgust:

"You're quite skilled in mathematics, but your handwriting is terrible. Even my six-year-old writes better than you! I'll bring you some brushes, ink, and paper tomorrow so you can practice your handwriting properly. Aren't you ashamed of yourself...?"

"..."

Lin Chuan opened his mouth, but was speechless.

"When you told me before that you had a little knowledge of astronomy, geography, physics and mathematics, I was a bit skeptical. But now I have seen the true extent of your mathematical knowledge!"

"I wonder how much you've learned about astronomy, geography, and physics? It's not just a superficial understanding again, is it?" Yan Xiangshi asked.

"Master Yan, astronomy, geography, physics, and mathematics are all profound and complex subjects. I have only learned a little bit of the basics!" Lin Chuan said.

"Well, astronomy and geography are one thing, but what about physics? Is it a science or a set of techniques?" Yan Xiangshi asked.

"Well, I guess so!" Lin Chuan nodded.

"The principles behind all techniques are secrets passed down from one family to another. Do you really understand this, kid?" Yan Xiangshi asked with a skeptical look.

"Just a little bit!" Lin Chuan nodded with a smile.

"Heh, I don't know much about astronomy and geography, but I did stay at the Gongshu family's house for three years when I was young, so I have a smattering of knowledge about mechanical devices. Since you dare to boast like that, let's discuss the principles of these ingenious mechanisms today!" Yan Xiangshi said with a smile.

Lin Chuan glanced at the arrogant Yan Xiang and nodded with a smile:

"Since Lord Yan is so interested, I shall dare to discuss this with him!"

"Shall I ask first?"

"Please speak!"

"Liezi, Tang Wen, the chapter on the two children arguing about the sun, Lin Dalang must have read it, right? Lin Dalang, who do you think is right and who is wrong?" Yan Xiangshi asked with a smile.

"Grandpa, you're cheating!"

Yan Liuniang, who had been sitting quietly to the side, suddenly spoke up.

Yan Xiangshi gently patted his granddaughter's head and asked Lin Chuan with a smile:

"Boy, dare to answer?"

Lin Chuan shook his head:

"It's not that I dare not answer, but I'm afraid Lord Yan won't believe me!"

Tell me about it!

"From my perspective, the morning sun and the midday sun are actually about the same distance from us!" Lin Chuan said.

Yan Xiangshi asked in surprise:

"What does that mean?"

"Well, this is complicated to explain! It can't be explained in a short time. I'll explain it to Master Yan in detail when there's another chance!" Lin Chuan thought for a long time, but still shook his head.

There is actually a scientific explanation for this in modern times, but it is difficult to explain clearly to a fortune teller.

"Lin Dalang, are you so sure?" Yan Xiangshi asked.

"Definitely!" Lin Chuan nodded.

"I await your explanation; it's your turn to ask!"

"I'd like to ask you, Master Yan, if two stones, one large and one small, were to fall together from a ten-zhang-high city wall, which stone would hit the ground first?"