Chapter 526: 526 The Sun Zi Mathematical Classic

Next to the Li family’s house lived another family in a mud-brick courtyard, impoverished to the extreme.

Generally speaking, in this village other than the grand residence of the old scholar, only Lizheng’s house was somewhat decent in appearance, everyone else was poorer than the next.n/ô/vel/b//in dot c//om

An old woman sat in the dusty courtyard, smoking a pipe stuffed with crude tobacco, puffing away.

The smoke was very strong and harsh, probably the cheapest tobacco leaves.

Feeling the gaze from the outside, the old woman lazily lifted her eyelids, took a cursory glance, and then continued puffing on her pipe, paying them no mind.

“Seems like most of the villagers are elderly.” Bai Youwei whispered to Shen Mo.

Whether it was the old scholar, Lizheng, or the Ma family, they were all people around seventy or so.

And even Lizheng’s son and daughter-in-law they had seen in the hall were in their early forties. If there were any younger, they were just children. Oddly, there were no youths in their teens or twenties.

“In such a remote and poor place, which youngster would choose to stay?” The old woman in the yard suddenly said, “Those who could leave, have already left. The only ones remaining are the elderly who cannot move, and the old bachelors who can’t get married.”

The group was taken aback, not expecting this NPC to offer information so readily.

Du Lai stepped into the yard and politely asked, “Do you know the Li family next door?”

Hearing this, the old woman laughed silently, wrinkles on her face like deep-set crevices, exuding an extremely unsettling feeling.

At that moment, a fit of coughs echoed from within the house, followed by an old man’s voice:

“I’ve been ill for so long, when will my daughters come to see me?”

The old woman took another drag from her pipe, gently knocked it against the ground, and said to the old man in the house: “Didn’t your eldest daughter come to see you just yesterday?”

“Why don’t all three of them come to see me together?”

The old woman scoffed, replying, “That’s not easy. The eldest returns every five days, the second every four days, the youngest every three days. Who knows when they’ll be able to see you again together.”

While chatting, her gaze shifted to Du Lai, and behind him to Fu Miaoxue, Shen Mo and Bai Youwei.

Everyone then understood, this NPC was challenging them with a riddle.

Bai Youwei breathed a sigh of relief inside.

Thank goodness, this wasn’t a difficult challenge.

She asked the old woman, “When were the three daughters last together?”

“They met during the Mid-Autumn Festival.” The old woman responded.

“How many days have passed since the Mid-Autumn Festival?” Bai Youwei asked again.

The old woman laughed coldly, “I’m old and forgetful, I can’t remember clearly….”

Bai Youwei slightly wrinkled her brow.

Not just her, Shen Mo and Du Lai frowned too.

“What’s the matter?” Fu Miaoxue was confused, “Is the riddle too hard?”

“It’s not that the riddle is difficult, we’re just missing something,” Bai Youwei explained, “This is an old riddle from Sun Tzu’s ‘Arithmetical Classic’, asking about three daughters: the eldest returns home every five days, the second every four days, and the youngest every three days. After the three daughters leave home together one day, on what day will they meet together again?”

“How many days?” Fu Miaoxue blurted out.

Bai Youwei: “Sixty days.”

The number of days is derived from finding the least common multiple between the intervals the daughters revisit home.

That is, multiplying the numbers 3, 4 and 5, and it’s 60.

Fu Miaoxue blinked and said: “Then just tell her the answer.”

Du Lai grabbed her hand and moved her behind him, “What’s missing here is the precondition – we don’t know on which day the three daughters left together.”

“There should be clues nearby for the Mid-Autumn Festival,” suggested Shen Mo, “Let’s split up and look.”

Once they figure out when the Mid-Autumn Festival was in this game, they could calculate when the three daughters will return home together next.

Fu Miaoxue complained, “Why go through all that trouble~”

After saying that, she bounced up to the old woman: “Hey, your three daughters will be back tomorrow~”