My sister, whom I raised, has turned evil after faking her death for three years.

In the days that followed, Su Qing's life was filled with two things.

Cooking and doing homework.

Putting aside the cooking for now, most of the eggs in the carton in the refrigerator perished within just one week.

The math matter is more urgent.

Jiang Ran's entrance exam is scheduled for next Wednesday, leaving Su Qing with only ten days at most.

During these ten days, Su Qing discovered a fact that both pleased and subtly frustrated her.

Xiao Ran is a genius.

On the first day, Su Qing sat at the coffee table in the living room, with a first-grade math textbook spread out in front of her, and taught Jiang Ran addition and subtraction within ten.

Jiang Ran sat quietly next to her, holding the lop-eared rabbit in her arms. She nodded every time Su Qing explained a point of knowledge, her expression as serious as if she were listening to some major scientific discovery.

"What is three plus five?" Su Qing asked.

  

Jiang Ran thought for a moment, lowered her head to count on her fingers, then looked up and whispered, "Eight."

Su Qing nodded, turned the page, and began explaining addition with carrying.

Following the teaching approach provided by the system, she used apples as an example: three apples plus nine apples, first make nine to make ten, then two are left over, so it's twelve.

Jiang Ran tilted her head and thought for a few seconds, then asked a question that made Su Qing feel a little uneasy: "Sister, what if it's one hundred and thirty-five apples plus two hundred and sixty-seven apples?"

"...That's second-year material."

"Oh." Jiang Ran obediently responded, took the pen from Su Qing, and slowly wrote the answer on the blackboard: 402.

Su Qing stared at the number, remained silent for three seconds, and then asked the system in her mind, "Was she guessing?"

The system replied in its usual calm tone: [No.]

[Analysis shows that after hearing the principle of addition with carrying, she mentally deduced the rules for adding hundreds digits.]

[Host, Jiang Ran's learning talent is rated A+. For reference, the average rating for children of the same age is C. You are rated D.]

"...The sentence after that doesn't need to be added."

The next day, Su Qing began teaching subtraction. She explained subtraction with borrowing once, and Jiang Ran nodded to indicate that she understood. Then she opened her workbook and completed all the questions on that page.

Su Qing checked it once, and it was all correct.

She closed the workbook expressionlessly, picked up the third-grade textbook, and turned to the chapter on fractions.

What is one-half plus one-quarter?

Jiang Ran thought for a moment: "If you turn one-quarter into half of one-half, then it's two-quarters plus one-quarter, which equals three-quarters."

Su Qing opened her fourth-grade textbook.

Word problem: Chicken and Rabbit in the Same Cage.

Su Qing stood in front of the small blackboard, holding a marker, took a deep breath, and began to draw according to the ideas given by the system.

First, draw ten circles to represent heads. Then, draw two feet under each head. Count how many feet are left unassigned and add the remaining feet two at a time under some of the circles.

"Sister," Jiang Ran raised her hand, her voice soft, "can I use subtraction? Let's assume they're all chickens, that's twenty legs. Actually, there are twenty-eight, eight short. Rabbits have two more legs than chickens, so eight divided by two equals four rabbits and six chickens."

Su Qing's hand, holding the marker, hovered in mid-air.

She looked down at the ten circles she had drawn and the feet scattered all over the blackboard, then at Jiang Ran's blinking, innocent expression, and said, "...When did you learn multiplication and division?"

Jiang Ran hid her face behind the rabbit, only revealing half of her face and a pair of smiling eyes: "Yesterday when my sister was cooking, I flipped through that third-grade math book."

Su Qing put down the marker, rested her hands on the coffee table, and remained silent for a long while with her head down.

The system spoke in her mind: [Host, your heart rate is rising. Are you angry?]

"No," Su Qing answered in her mind.

[Is that frustration?]

"No, not exactly."

She looked up and saw Jiang Ran looking up at her, waiting for her to explain the next question. Her eyes were bright and a small smile was playing on her lips.

Su Qing reached out and ruffled her hair, her tone carrying a hint of barely perceptible pride: "You're amazing."

Jiang Ran stumbled forward as Su Qing rubbed her, but she didn't flinch. Instead, she squinted and nuzzled her head into Su Qing's palm.

I felt really happy.

Her older sister praised her.

My sister said she's amazing.

She wants to learn more math problems so that her sister will praise her every day.

While taking a walk in the park downstairs in the evening, Su Qing was still immersed in the daze of "my child is a genius".

Jiang Ran held her hand, carrying the rabbit in her other hand, and every few steps she would look down to check if her shoelaces were untied.

Cheng Xiaoyu had been squatting by the slide for a long time. As soon as he saw them, he sprang up and rushed over like a cannonball: "Pretty sisters! Little Ran! I've been waiting for you for so long!"

He ran up to Jiang Ran, pulled something out of his pocket, and handed it to her: "Here you go! I bought this at the school gate today, it's strawberry-flavored hard candy, my mom said it's really delicious!"

Jiang Ran looked at the candy that Cheng Xiaoyu had squeezed so tightly it was almost melted, then looked up at Su Qing.

Su Qingchong nodded.

She took it, unwrapped the candy, and put it in her mouth.

The sweetness of strawberries melts on the tip of your tongue.

"Thank you." Her voice was still not loud, but it was very clear.

Cheng Xiaoyu scratched the back of his head, grinned, and revealed a missing front tooth.

When he said thank you last time, Jiang Ran only nodded slightly, but this time she actually spoke! He took another step forward: "Let me tell you, something super funny happened in our class today..."

He chattered on about the funny things that happened at school, and Jiang Ran listened quietly, nodding occasionally and sometimes raising the corners of her mouth slightly.

Although she still doesn't speak most of the time, compared to her tense state a week ago, Su Qing could tell that she had slowly begun to get used to Cheng Xiaoyu's presence.

She leaned back on the bench, crossed her legs, and thought to herself, "It's good to have friends now."

Not long after, Su Qing was looking down at her phone when a familiar voice came from beside her: "Su Qing? What a coincidence, we've run into each other again."

Su Qing looked up and saw Sun Yaqin standing next to the bench, holding two cups of milk tea in her hands.

She wore a linen shirt today, her hair was loose over her shoulders, and the fine lines at the corners of her eyes were still so beautiful when she smiled.

Then she turned to Su Qing, pointed in Jiang Ran's direction, and said with a hint of surprise, "So the little sister Xiao Yu talks about every day, Xiao Ran, is your sister!"

Sun Yaqin showed no surprise whatsoever; on the contrary, she was quite delighted.

"By the way, have you been working on math problems lately? Have you encountered any difficulties? I'm the kind of person who likes to teach, so feel free to ask me anything you don't understand."

As she spoke, she handed a cup of milk tea to Su Qing.

Su Qing initially wanted to refuse, but seeing Sun Yaqin's gentle gaze, she accepted it anyway.

"Thank you, Sister Yaqin."

Su Qing bit her straw, thinking to herself that Sister Yaqin was really kind-hearted.

The system's voice suddenly sounded in his mind: [Host, based on cross-referencing all the previously collected data, I now have enough information to correct a cognitive bias.]

[The probability that Sun Yaqin is Cheng Xiaoyu's sister is 0.001%, and the probability that she is his mother is 99.99%. Her actual age is approximately forty.]

DNA analysis shows that she and Cheng Xiaoyu are directly related by blood.

Su Qing stopped biting the straw.

Her gaze swept back and forth between Sun Yaqin and Cheng Xiaoyu, then swept over them again.

Cheng Xiaoyu was standing on tiptoe to reach the milk tea in Sun Yaqin's hand, shouting, "Just one more sip, just one more sip!" Sun Yaqin held the milk tea up high and scolded him, "Your voice is hoarse from shouting and you're still drinking iced milk."

This scene looks exactly like a mother taking care of her son.

Forty years old...

Su Qing lowered her head and took a sip of milk tea to process the information.

She recalled that when they first met, Sun Yaqin said, "I'm here to buy some materials for my brother." Today, she said, "I like to teach others." From beginning to end, she was creating the persona of a "young older sister."

Su Qing didn't think it was a big deal. After all, what girl doesn't want to look young?

The fact that Sister Yaqin is willing to go to this trouble shows that she cares about this, so I'll just cooperate.

Moreover, Su Qing felt it was amazing that someone could maintain such good looks at forty.

"Sister! Sister!" Cheng Xiaoyu suddenly popped out from under Sun Yaqin's arm, his voice so loud it could be heard throughout the park, "Look over there! I can climb up!"

He ran to the climbing frame next to him, stepped onto the first horizontal bar, and started climbing. Halfway up, he suddenly turned around and shouted at them, "Sis—look how high I've climbed!"

He pronounced the word "sister" a bit too forcefully, as if he were reciting an unfamiliar word.

The system spoke in Su Qing's mind: [When Cheng Xiaoyu called Sun Yaqin "sister," his tone was 0.8 octaves higher than usual, and the duration of the pronunciation was 0.3 seconds longer. This is a typical vocal characteristic of being forced to lie.]

Su Qing looked at Cheng Xiaoyu's chubby figure swaying back and forth on the climbing frame, and then at Sun Yaqin standing beside him, nervously spreading her arms, ready to catch him at any moment. She suddenly found it a little funny.

This mother and son had a tough time both of them trying to maintain the "sibling" persona. One was forced to call the other "sister," and the other was forced to pretend to be calm.

Su Qing lowered her head, took a sip of milk tea, and smiled slightly.

Oh well, as long as everyone's happy.