Same day at classroom, Ms.Song writes some question about math. She stare at her students looking for someone to came forward.

"Any participants?" Ask Ms.Song making all students looked away hoping didnt get picked. But, before Ms.Song called a student, Ms.Song saw Seohyun raised her hand

"Okay Seo, can you solve question number 1?" Ask Ms.Song while gave the chalk to Seohyun

"Hmm..everything is okay for me" said Seohyun calm and started to do her job

Ms.Song impressed by the way Seohyun do the abacus and counts it fastly, the other students jaw-drop when saw and realized Seohyun counts so fast, do the abacus perfectly, finish it in 1-2 minutes, plus her answer are correct and she do the explanations too. Ms.Song clapped her hands and the students followed felt impressed. Seohyun take a sit and high fived with Krystal her seatmates.

"Any body want to solve number 2?" Ask Ms.Song and saw Sulli raised his hand 

"Okay Ssul, solve that....if you can" said Ms.Song feel weird

Sulli just nod and started to solve, while Ms.Song and the other student except Yoona stared at him in disbelieve. Sulli who used to sleep during lesson, raise his hand up and came forward? Wow world going to be in war, they thought. Back to Sulli.....Sulli solved it easily and writes the answers confidently. Sulli finished in 4 minutes with correct answer and a little explaination. The whole class except Sulli and Yoona jaw-drop plus eyes widened didnt believe what just they saw on the board. Some students turn their head to Sulli with are-you-kidding look and Sulli just eye smiling then high fived with Yoona. Seohyun and Krystal saw the duo and glances to each other like about to war.

"You can do the number 3? Can you?" Ask Seohyun in whispered tone to Krystal

"Mmm....okay, trust me unnie we will beat those pranksters" whispered Krystal and the two smiling then look the duo again.

Ms.Song clear and start to speaking again.

"Number 3? Any-" got cutted Ms.Song by Krystal who smiling brightly

"I will do that miss" said Krystal and her unnies except Seohyun give an are-you-kidding look

"Okay Krys, here the chalk" said Ms.Song and gave the chalk

Krystal just solved it with her own abacus learned from Seohyun. She writes down the explanations first then starts to count it with math formula of course. She counts in one by one, writes down the total, counts again, and finally write the answer correct and clearly. She smiles and take a sit on her desk. Ms.Song smile and nodded felt proud to her students, she dont know if those Sulli and Krystal came forward for an battle that only the four know. Krystal high fived with Seohyun and the two turn their head to saw the duo glared at them. The two giggled felt the victory in front of their eyes. Until..

"Number 4? Any-" Ms.Song got cutted again and saw Yoona raised his hand 

"Honestly, what are you two ate this morning?! Here!" felt upset Ms.Song and harshly gave the chalk to Yoona

Yoona starts to solved the question, but Yoona use abacus different from Sulli who didnt do abacus because he cant, so Sulli just writes and counts based only on formula. Yoona writes the formula first and Seohyun saw that she curses herself for not writes the formula. Yoona smirks and continue writes the formula, then explanations, counts the total, divide the total, and writes the answer. Yoona finished in 2 minutes and gave back the chalk to speechless Ms.Song and walked back to his seat. He stopped at Seohyun desk.

"Ms.Seohyun finally i beat you...hahaha" said Yoona then evily laughed like alligator while take a sit on his desk. Seohyun froze and Krystal stare at her while shaked her head slowly didnt believe if her unnie got lose by a immature boy like Yoona.

Yoona and Sulli high fived, fist bumping, and danced in victory. The four who battling intensely didnt believe win/lose by small things like forgot to write the formula. 

1 hour passed and class diamissed to the next class......science class. The four tell the whole story, the boys laughed so hard when knew about Seohyun one of the top student lose to Yoona the immature boy just because forgot to writes the math formula. While the girls prepared to take revenge in the next class after 10 minutes break. Score now 1 for boys, 0 for girls.