In a World of Reversed Chastity, I’m Rumored to Be an Easy Bitch (♂) Among Lustful Girls - 54

Chapter 54: The Thing That Turns a Capable Child Into an Incapable Child

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“―So, this sigma( ∑) thing is the sum of all the numbers in a sequence.”

“That’s what it meant!? That’s super simple, you should’ve just said so sooner!”

Pushing aside all kinds of temptations, we finally started studying math.

Since Ayame-san had taught me about this recently, teaching Riria helped me review the materials again as well. It might actually be a two-birds-with-one-stone kind of study method.

“Huh… So that’s the meaning ∑ ….”

“Come on… Didn’t the teacher hammer that into us during math class…? You don’t remember?”

“Well… I’m not really into sour things… I prefer stuff that’s bitter and gooey, you know?”

“…. Right. I was an idiot for even asking.”

“But now that I know what it means, these things feel much easier now. Basically, I just have to add all these numbers together, right?”

“Pretty much, yeah.”

“But why use a complicated letter like ‘∑’? When I first saw it, it just looked like one of those clips that close bread bags.”

“I mean… Yeah, I can kind of see it.”

“By the way, those are called ‘bag closures.'”

“Why do you know the name for bread bag clips but not what ∑ means…?”

“Now that you mention it, ‘bag closure’ is just straight English. Saying 𝓑𝓪𝓰 𝓬𝓵𝓸𝓼𝓾𝓻𝓮 actually feels more natural.”

“Why is your English pronunciation so unnecessarily good?!”

While being thrown off by Riria’s unexpected English skill, I continued studying. Understanding what ∑ meant when dealing with sequences was a huge step forward. Knowing it versus not knowing it made a massive difference in understanding the lesson.

“Alright! Now that we know that, time to add up the numbers! Uh, one plus two plus three plus…”

“Um…. Sotogahama-san?”

“What?”

“No, not ‘what’… Are you seriously trying to add them all one by one?”

“Yeah, because we’re supposed to add all the numbers in the sequence, right?”

“Nobody actually adds them all one by one like that!”

Why was she using a brute-force method of adding each number individually when calculating a total sum in math…? Well, technically, if you took your time and made no mistakes, you’d eventually get the right answer, but still….

Could it be that this girl also calculates probabilities by listing out every single possible outcome? If you tried that during a test, you’d run out of time in no time. Even a “Hundred-Million Years Button” from a certain novel wouldn’t be enough.

“Listen. There’s a way to calculate this more efficiently.”

“You should’ve told me that first!”

“I mean, most people should know this already, so…”

“I’m an idiot, okay?!”

“Alright, alright. I’ll explain it in a way so even an idiot like you can understand. Listen up now.”

This sequence was super simple: the first term was 1, the common difference was 1, and there were 99 terms. In short, it was just the integers from 1 to 99 lined up in order. The problem was asking us to add all those integers together. Riria’s method of adding them one by one wasn’t wrong, but there was a much smarter way to do it.

“Sotogahama-san, what’s 1 plus 99?”

“Are you making fun of me? Even I know that’s 100.”

“Right. Then what about 2 plus 98?”

“Also 100.”

“Then 3 plus 97?”

“100.”

At that moment, Riria let out a small “Ah!” She seemed to have realized something.

“…If you add the numbers from the front and back of the sequence together, you get a bunch of hundreds!”

“Good catch.”

“So if you keep doing that, there would be… Forty-nine hundreds! And one 50 left over!”

“Exactly. So when you add all that up?”

“4,950! You’re amazing, Hirakawa-kun!”

“This method is the basis for the formula shown in the textbook.”

“Whoaaaaa!!! I feel like I can actually do math now!”

Riria looked overjoyed, practically radiating brain chemicals. I knew that feeling—solving something on your own felt amazing. It was a different kind of pleasure from doing something naughty. I totally got it.

After that, every time I explained the meaning of a letter or a symbol, Riria solved another problem, like when the perfect piece in Tetris finally dropped. She kept making rapid progress in math.

Maybe she wasn’t inherently dumb. Maybe she actually had good instincts, but when she stumbled over something, she’d freeze and refuse to move forward.  Yeah. It seemed Riria was that kind of person.  So if I explained the unclear parts slowly and clearly, she would pick right back up like it was nothing.

I see, I see… Teaching someone like this could actually be fun too…!

“―Whoa, I solved all the practice problems in the textbook!”

“Nice going, Sotogahama-san. At this rate, you might not just avoid repeating the year—you could even rank pretty high.”

“Ehehehe… I knew it, I’m a kid who can do it if I try. Yup yup.”

“Alright, let’s keep the momentum going. Not just math. Next up is chemistry.”

“Wh-what!? If you cram too much into me at once, all the stuff I just learned about sequences is gonna fall right out!”

“You’re like one of those stackable rocket pencils…”

Well, to be fair, we had been studying non-stop for about two hours, so maybe it was time for a break.

Even fools need to rest sometimes. Probably. I dunno.

“Alright then, let’s take a little break. I’ll go grab us something to drink.”

“Thanks!”

I headed to the kitchen and opened the fridge. If I remembered right, Riria liked carbonated drinks. Grabbing a couple cans of Mountain Dew from the back should do the trick. I grabbed two ice-cold cans.

They’re chilled to perfection…! Thank goodness…!

Holding the cans, I headed back to my room on the second floor and opened the door with a click.

For some reason, Riria whipped around to face me with a startled expression. She was holding something in her hands, trying to hide it from my view.

Suspicious… Very suspicious…

“W-welcome back, Hirakawa-kun…”

“Sotogahama-san…? What were you doing?”

“N-nothing at all?”

“You’re acting suspicious!”

Curious about what she was hiding, I leaned in to peek, but Riria clearly didn’t want me to see and kept hiding it. Refusing to back down, I pushed even harder. Eventually, I caught a glimpse of what she was holding—a cookie tin.

Ah, and inside that cookie tin… There was that. It’d be bad if she saw that…

“…Sotogahama-san? You… Saw what’s inside that cookie tin, didn’t you?”

“I-I didn’t! I totally didn’t!”

“I see… So you didn’t see.”

“Y-yeah, I wouldn’t just peek into someone’s stuff without permission, right?”

“Oh really… By the way, how many millimeters was it?”

“It’s super rare to find something so thick, right? Like 0.1 millimeters… Ah.”

And just like that, she blew her cover in the dumbest way possible. She probably got hungry and reached for the cookie tin on impulse. I really screwed up hiding it there.

Ahhh… Now how do I even explain this…?

While I was desperately thinking that over, Riria suddenly tackled me onto the bed.

“You were expecting this, weren’t you? Otherwise you wouldn’t have hidden something like that, right?”

“W-wait, it’s not like I bought that myself or anything…!”

“Who cares about that? It’s so rare to find one that thick… I’m curious how it feels too. Let’s try it out.”

“Yo-You said we were going to study today…”

“This is studying! It’s time for health and physical education lessons!”

Like hell it is!

Even so, I couldn’t stop the switched-on Riria, and soon she was tugging my clothes off.

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