His teasing tone annoyed her. Jiyeon took a deep calming breath before speaking in a low, quiet tone, "I did have fun. And thanks to you. Now go back to your seat."

She noticed the corners of his mouth lift up, a smirk playing upon his lips. "Did he kiss you? He kissed you, didn't he? Is he a good kisser?" Taeyong whispered in the same teasing tone.

Jiyeon her teeth and let out an annoyed sigh. "You're too nosy." Her eyes narrowed. "Go back to your seat!" she demanded firmly and gestured him to his seat.

"You're too bossy." Taeyong turned around and put the calculator on Eunkyo's table on his way back to his seat.

After taking a deep breath, Jiyeon turned her attention back to the class. "Okay, class, let's continue," she said, and for a moment the classroom was filled with the sounds of students grabbing notebooks and pencils.

"Our number system has many unusual features, which are often well hidden. Discovering them can certainly be a rewarding and entertaining experience. Sometimes I just stumble onto these relationships, while at other times the discovery of these relationships is the result of experimentation." She turned to the blackboard and wrote the following relationship on the board:

81 = (8+1)² = 9²

Jiyeon looked back at the class. "Can anyone describe what's going on here?" she asked, pointing at the number relationship she had written on the board.

Only one hand was raised, and Eunkyo spoke, "You have taken the square of the sum of the digits."

"That's correct." Jiyeon smiled. "Here's another such example." She wrote it on the board:

5,832 = (5+8+3+2)³ = 18³

With her body facing the blackboard, she turned her face towards the class and explained, alternately pointing at the first example and the second example, "In both cases, I have taken the sum of the digits to a power and ended up with the number I started with. Trying to find each such number relationship is no mean feat. For example—"

82 ≠ (8+2)² = 10² = 100

Jiyeon circled the "82" and "100" she had written, saying, "Does not follow this pattern."

"That's so astonishing," said several students, followed by Taeyong's prideful scream, "Youngest teacher, I've discovered one!"

She clapped her hands together to knock the chalkdust off them as she made her way to him. Taeyong tapped the eraser end of his pencil lightly on the notebook, a bright smile illuminating his face. Jiyeon took a look at his work.

512 = (5+1+2)³ = 8³

She blinked in surprise. Taeyong seemed to completely understand the concept instantly. "Good job." Jiyeon patted his head lightly. "Numbers can be fun too, right?"

Taeyong nodded. "I can't believe I'm saying this, but I enjoy your class!"

"I'm glad—"

"Miss Park, I've found two unusual numbers," the male student sitting in the row ahead of Taeyong, said, his voice rising with excitement.

Jiyeon stepped towards him and looked down at his notebook, checking his work.

17,576 = (1+7+5+7+6)³ = 26³       2,401 = (2+4+0+1)⁴ = 7⁴      

"Great job," she said, giving him a pat on the back, followed by a thumb up.

"The beauty is self-evident." His face broke into a big smile. She nodded in agreement with his statement.

As Jiyeon made her way back to the blackboard, other students asked her to check their works, enthusiasm lacing each of their voices. No doubt, the students, including the ones who found her class boring, enjoyed her class today. Immediately, a deep feeling of satisfaction settled within her. With a bright smile decorating her face, Jiyeon wandered throughout the room, checking the students' works. She praised the students who discovered the unusual number by saying 'good job,' and encouraged the students who hadn't yet discovered one by saying 'don't give up, keep experimenting' while giving them a light pat on the arm.

The students lapsed into silence when she stood at the front of the classroom. Jiyeon cleared twice. "I'm going to teach you a number trick. My trick is no illusion. It's real," she began, seriousness creeping into her voice.

They looked quizzcally at each other and then back to her, who said, "Whoever can figure out my trick and then come up with a mathematical explantation, I'll raise their math grade one whole letter grade."

Everyone let out a resigned sigh. They seemed to believe that Eunkyo was going to get it. After all, she was the class math whiz.

"It's not fair. Eunkyo has a 100 average," mumbled several students. "We might as well not even try."

Eunkyo rolled her eyes. "I'm not smarter than you guys. I just love math."

Eunkyo's words brought a smile to her lips. "I said whoever can figure this out will get their grade raised, not the first person to figure it out," Jiyeon clarified. "Are you ready now?"

"Yes, we're ready!" everyone shouted.

Jiyeon went to her desk and opened her bag. She pulled out a piece of paper, ripped it up into small pieces and wrote a three-digit number. "I'm writing a three digit number on a small piece of paper," she announced, "and I'm going to put it into one lucky student's pocket." Her eyes scanned the classroom in search of the lucky student.

"Youngest teacher, what are you going to do actually?" Taeyong drummed his fingers on the table.

Rolling the small piece of paper into a tiny ball, she made her way to Jihoon, the one who had punctured her bike tire. She handed the tiny ball to him, saying, "Put this into your pocket and don't open it until I ask you to."

"Okay, miss Jiyeon." Jihoon put it into the pocket of his school uniform shirt.

Bending close to him, Jiyeon whispered into his ear, her tone taking on a sharp edge, "Why did you damage my bicycle tire?"

She could see his hands trembling slightly. He clasped them together to quiet the shaking. He ducked his head down, stammering, "I-I'm so sorry...I will return your bike to your house after school."

She took a deep breath to calm herself as she walked back to her desk. "I need a volunteer, someone who's very good with numbers and calculations." Jiyeon sat down on the chair and looked at Eunkyo. "Eunkyo, how about you?"

Eunkyo jumped up excitedly and ran to the front of the room. "I'm ready." She picked up a piece of chalk.

Jiyeon leaned back in the chair, crossed her arms under her s and closed her eyes. Jaehyun's face filled the screen of her mind again. She couldn't help but smile. Focus on teaching, Jiyeon. She nodded, agreeing with her inner voice. "Eunkyo, write down a number between 500 and 1,000 and don't tell me what you have."

The scraping of the chalk was loud in the silence.

"Now add 733, please."

"I'm done."

"Now that you have a four digit number, go ahead and earse the first digit and add that to the new three digit number. For example, if you have 1,377, erase the 1. That leaves 377. Add the 1 to 377. That equals 378. Are you with me?"

"Yes, Teacher Park," Eunkyo replied, followed by the sound of chalk scraping on the board.

"Now subtract that number from the one that you picked first," she instructed, keeping her eyes closed. The screech of chalk scraping assaulted her ears.

"Are you finished now?" she asked.

"Yes!" Excitement rose in Eunkyo's tone. Jiyeon opened her eyes and took a look at her work on the blackboard.

679 + 733 = 1,412

1 + 412 = 413

679 - 413 = 266

The "266" had been circled.

Jiyeon shifted her gaze to Jihoon and instructed him to pull out the tiny ball paper from his pocket. All eyes were on Jihoon. He pulled it out, unrolled it and announced loudly, "266!"

Almost all of her students were amazed at her trick. They began asking a lot of questions. Avid curiosity filled their voices.

"How did you do that?"     "How did you know?"     "What's the secret?"     "Are you a teacher or magician?"     "Do you get 266 every time?"

Jiyeon ignored all the questions except the last one. "It doesn't yield 266 every time. Here, I'll show you."

Jiyeon jotted down 408 on another small piece of paper and rolled it into a tiny ball before anyone could see what the number was. She rose to her feet, walked over to Eunkyo and placed the tiny ball into the pocket of her uniform shirt. She took steps backwards and sat down on the edge of her desk confidentially, her eyes fixed on Eunkyo.

"Now Eunkyo, pick a number between 500 and 1,000. Please choose a number different from the first one. It will work with the same number, but it is better to have a different number."

Eunkyo picked 867 this time.

"Now add 591."

Eunkyo made the calculations: 867 + 591 = 1,458

"Remove the 1 and add it to the units digit of the sum."

She did as she was told: 1 + 458 = 459

"Then subtract that number from your original number."

867 – 459 = 408

Eunkyo finished by circling the "408" she had written.

Jiyeon instructed her to pull out the tiny ball paper from her pocket. Eunkyo turned to face the class, and all eyes were fixed on her. She pulled out the tiny ball paper, unrolled it and shouted, "408!" She held it up, showing it to the class.

Taeyong looked at Jiyeon with his mouth open in amazement. His voice contained a thread of impatience as he spoke, "Youngest teacher, just tell us how you knew that the answer would be 408."

A couple of students followed suit, chanting, "Just tell us right now, come on!"

"It's easy, guys," Eunkyo said. "The key factor is how much our magical teacher adds to my original number."

"Kyokyo, can you explain mathematically how it works?" Taeyong challenged.

"I'm lazy, Yongyong." She walked back to her seat. The other students snickered at her answer.

Taeyong made a tsk-tsking sound, shaking his head. "Just admit that you can't, lazy ," he retorted, a trace of mockery lacing his voice. Eunkyo stuck out her tongue at him and sat back down.

"Okay, class," Jiyeon announced, clapping her hands together. The students turned their attention back to her. "I'm going to explain why this works as it does." She went to the blackboard and retrieved a piece of chalk.

"For every picked number between 500 and 1,000, you will always get a 1 in the thousands place when this number is added to 591. Dropping the 1 and adding it to the units digit is tantamount to merely subtracting 999 from the number. That is,"

-999 = -1,000 + 1

"If I now represent the picked number as y, then what is being done is,"

y - (y + 591 - 999) = y - y - 591 + 999 = 408    

Jiyeon circled the "408" she had written on the board before she turned to face the class. She spoke slowly and patiently as the students took notes, "Remember, the letter y represents the number randomly picked. As Eunkyo said, the key factor is how much I add to the picked number. If instead of adding 591, I added 777, then the result would always be 222, regardless of which number my volunteer chose between 500 and 1,000. The picked number cannot be less than 500, or else you might not get a sum in the thousands, and at the same time the picked number should not be greater than 999, or you might get a 2 in the thousands place, which would ruin this scheme."

The class erupted in applause and loud chatter about how easy her trick was. A proud smile lit up Eunkyo's face as she said, "I told you so."

"Well, Kyokyo, you're a genius," Taeyong responded, his voice dripping sarcasm. Glancing at him, Eunkyo put her thumb and index finger to form the shape of an L on her forehead to indicate the word, "loser."

Jiyeon firmly clapped her hands together and everyone fell silent. She smiled. "I'm going to share some easy yet impressive mental calculations that you can learn to do immediately."

The students raised their eyebrows and nodded enthusiastically.

"Let's begin with how to multiply any two-digit number by eleven in your head. It's very easy once you know the secret—" Jiyeon was interrupted by the sound of the bell ringing, indicating a change of period.

Groans of disappointment filled the classroom. Jiyeon grabbed her bag from the desk and slung it over her shoulder, "I'll share the secret next time. Bye, class." She walked out of the classroom. She continued to have a smile on her face as she headed towards the next class. She felt proud that she could have gotten Taeyong and his classmates interested in her class.

Jiyeon entered the classroom and scanned the class when everyone greeted her. She greeted back with a smile as she walked over to her seat and placed her bag on the desk. She decided to share the tricks of mental calculations because it helped her forget her personal problems. She started with multiplying two-digit numbers and higher-digit numbers by eleven. The students were actively engaged with her and impressed with her tricks. She continued with squaring two-digit and three-digit numbers until the bell rang, signaling recess. Students thanked her politely and rushed out of the classroom.

Jiyeon chose to saty in the classroom than go to the staff room. She propped her elbows on the desk and rested her cheeks on closed fists, staring at the empty room. She was still in no mood to confront Mrs Kim. Mrs. Kim might bombard her with questions like why she didn't come to her house yesterday.

"Stop avoiding her and confront her," Baekwoon's voice echoed in her head. "Don't be disrespectful to elder people."

"Keep your big snoot out of my business," Jiyeon muttered as she folded her arms on the desk and rested her head on them. Her eyelids felt heavy. Closing her eyes, she let herself drift off.

She felt someone shake her shoulder. "Wake up, recess is over," came a familiar woman's voice. Jiyeon opened her eyes, lifted her head from the desk and blinked, trying to clear her vision. To her surprise, she found Yoona stand in front of her, holding the Chemistry book against her chest, while the students sat neatly at their desks, ready for the lesson. 

Jiyeon gulped and then sprang to her feet. She looked at the students. "Why didn't you guys wake me up earlier?" she scolded them.

They ducked their heads down. "We didn't dare," some students said in unison, while the others stayed silent.

Yoona shook her head, smiling before she moved to stand beside her. "Let's go to Heartful Café after teaching," she whispered in her ear. "Jaeko wants to meet you. He said he has something to show you."

"He has something to show me? What is it?" Jiyeon questioned in a low, quiet tone, her brow furrowed in obvious confusion. "I only met him briefly once."

"I don't know what it is, but it's something related to my deceased nephew," Yoona answered.

Jiyeon bit her lower lip, thinking. Her mother made her feel so trapped. She was actually no longer interested in anything related to Baekwoon, but Yoona might be able to convince her mother to let her go. She really wanted to spend time with Jaehyun again.  

She took a deep breath and leaned closer to her ear. "I want to go with you, but my mom will pick me up after teaching," Jiyeon whispered. "Will you help me convince her to let me go?"

"You don't need to worry, I'll help you." Yoona squeezed her arm gently. "You better go to your class now. You know you interrupt my class."

Yes, she'll help me! Jaehyun, we can spend time again. A surge of excitement rushed through her at the thought. Jiyeon wanted to jump into Yoona's arms, to thank her, but she swallowed the urge. She bowed to the class and apologized, "I'm really sorry for interrupting you guys." She grabbed her bag from the desk. "Thank you, sis." She planted a light kiss on Yoona's cheek. Yoona's eyes widened a little, while the students gasped.

Smiling like an idiot, Jiyeon ran out of the classroom, heading towards her class. As she entered the classroom, the students stood up to greet her. She greeted them back as she walked over to her seat and placed her bag on her desk.

After the class settled down, she cleared and announced with a broad smile, "Okay guys, I have a great news for you!"

The excitement that spread through the students was palpable. Sohyun and Jaehyun couldn't sit still. Seemingly, they wanted to hear what the news was.

"We're going to have fun with math today," Jiyeon added, clapping her hands together excitedly like a child.

The entire class erupted into whispers, the disappointment clearly showing in their faces, except for Jaehyun and Chaeyeon, who were smiling at her. She sat down on the edge of her desk, staring sternly at the students. They lapsed into uncomfortable silence. She took a deep breath and gave them a smile, trying to relieve the situation.

"Let's begin with magically quick products," Jiyeon said softly, "I'm going to call you guys to the front of the classroom. Ask you for a two-digit number, and I select one. See who can multiply these numbers fastest. If you can figure out my trick, I'll do anything you ask me to."     

Excitement filled the room. Students began asking questions.

"Can we use a calculator?"     "Are you going to use a calculator?"     "Really you'll do anything we ask to?"

"You can use a calculator, but I'm not going to use one," Jiyeon answered. "Yes, I'll do anything, I promise."

"Including kissing us?" the fat male student with a shaved head, who sat in the back row, remarked aloud. The students snickered at him, except for Jaehyun. Her lover's eyes narrowed as he stared at her.

Jiyeon blew out a loud breath. "I'll do anything except that one," she firmly said. "Now come to the front."

The fat male student sparng to his feet and ran to the front. "I select 78," he said before she could even open to ask, punching his calculator with his index finger.

"I pick 80," Jiyeon responded, and quickly added, "6,240."

His mouth gaped open, and his unblinking eyes stared at her. "How could you multiply two-digit numbers faster than me who used the calculator?" he breathed out.

Jiyeon just smiled and told him to go back to his seat. She called out his seatmate with a blunt sugar-bowl haircut to come to the front.

"I choose 67." The blunt sugar-bowl haired student punched the numbers into his calculator.

"65." Jiyeon watched his index finger punch the calculator while doing the math in her head, and quickly said, "4,355."

He jerked his gaze from the calculator to her. "That's so cool!" His voice oozing amazement boomed. He muttered something in a low tone as he went back to his seat.

Jiyeon randomly called on students to come to the front. They were excited and amazed at her ability to multiply two-digit numbers faster than them who used the calculator. No one could figure out her trick yet. Now, there were ten students who weren't called yet, the three of them were Chaeyeon, Jaehyun and Sohyun.

Jiyeon looked at Sohyun, who had her elbow on the table, her cheek resting against her palm; her narrowed eyes were fixed on her. It looked like Sohyun still harbored resentment towards her for giving her an F grade on the test.

She drew a deep breath, trying to stay calm. "Sohyun, come to the front," Jiyeon said firmly.

"Be ready, Miss Park." Sohyun smirked. "I'm going to beat you."

"Go Sohyun! Go Sohyun! Go Sohyun!" chanted a couple of students while clapping their hands rhythmically when Sohyun rose to her feet and went to the front without bringing a calculator.

Sohyun looked at her sharply, saying, "89."

"91."

Just as the two-digit number came out of Jiyeon's mouth, Sohyun's stern and prideful voice boomed through the room, "8,099."

Jiyeon's jaw dropped, disbelief filtering through her, while the class erupted into claps and shouts, congratulating Sohyun for beating her teacher. She crossed her thumb and index finger to form a heart shape, a proud smile illuminating her face.         

Sohyun has figured out my number trick. Jiyeon blinked twice. "Sohyun, go ahead and explain my trick to your classmates."

Sohyun cleared , and everyone fell silent. Their eyes were focused on her, seemingly ready to listen to her explanation. 

"Guys, do you notice that our teacher selected a factor that is 2 from the number you picked, larger or smaller? She previously selected smaller, so I picked 89 since I was sure she would select larger—" Sohyun paused as her classmates whispered to each other.

Jiyeon put her index finger to in a gesture for 'quiet.' The whispers lapsed into silence.

Sohyun continued, "The trick is that the average of 89 and 91 is 90. 90 squared is 8,100, then subtract 1. That equals 8,099, which is the product of 89 and 91. Squaring two-digit numbers that end in 0 is very easy: just square the first digit and add two zeros. In other words, the trick is very simple; you just need to square the average of your selected number and our teacher's selected number, then subtract 1. That's it."

The silence quickly morphed to an eruption of hands clapping and faces smiling. Sohyun looked at Jiyeon, one side of curled upward before she went back to her seat. Then Jaehyun's hand shot up in the air.

Her heart skipped a beat as Jaehyun asked, curiosity lacing his deep voice, "Teacher Park, how could you square two-digit numbers that don't end in 0, say 79, so fast? Could you tell us the technique?"

The students looked at her intently, anticipating her response, except for Sohyun, who was busy scribbling in her notebook.

Jiyeon drew a deep breath and forced her skipping heart to calm. "Squaring two-digit numbers—"

"Miss Park, fulfill your promise first. You said you will do anything except kissing us," Sohyun interjected.

"Okay, what do you want me to do?" Jiyeon attempted to smile, the corners of twitching.

Sohyun stared intently at her, a trace of an evil smile on her lips. "I want you to dance right there." She pointed her index finger to the front of the class.