A/N: Wow…just wow. Absolutely no effort into this title. Actually, that's not true. After thinking of even shittier titles for about ten minutes I just decided to "fuck it" and named this Math. Because that's what this is about. Math. And a headcanon. And Zoro. Enjoy!

Usopp hadn't given it much thought when he first heard the swordsman mention numbers. Something about dividing an enemy pirate crew evenly between them –them being himself, Sanji, and Luffy. After all, it was a fairly simply three way division that involved fighting, something Zoro was basically a savant at. Usopp wouldn't have been the least bit surprised if Zoro somehow couldn't do the same exact division in a situation void of violence.

A few weeks later, as Usopp sat on the bow, he heard the heavy thud of boots trudge up the stairs and looked away from his notes to greet Zoro. The swordsman, acknowledging the hello with a yawn and sleepy wave, sat down with his back to the railing and closed his eyes. Usopp turned back to his notes and tried to calculate the minimal amount of wood and nails needed to patch up the Merry. Ordinarily this wouldn't be so difficult, but including the additional task of minimizing cost –something Nami demanded at all times- was proving to be a cumbersome task.

"What are you mumbling about?" Zoro suddenly asked, his voice at its usual, sleepy rumble.

"Sorry," Usopp replied. "I didn't realize I was thinking aloud. I'm just trying to figure out how much money Nami will need to give me for ship repairs."

He heard some shuffling and turned to the right and saw Zoro squatting beside him, looking over his shoulder at the notes. After five seconds or so, Zoro leaned back against the railing with a sigh. "3,000 berri should be enough. I image the witch wants it as cheap as she can get?"

"3,000 berri?" Usopp questioned. "Are you sure that's enough?"

"Yeah," Zoro nodded and closed his eyes. He folded his arms behind his head and settled back, as though the matter was settled.

"How do you know?" Usopp asked, wondering if the swordsman was purposefully skimping on the building supplies so he could possibly get a larger allowance for liquor.

"Because it's the right answer." Zoro shrugged, without opening his eyes.

"Explain it to me."

Zoro released a heavy exhale and began. "Well, you need 13 large boards right? You wrote they tend to be about 175 berri each. And 6 smaller boards at 100 berri each puts total wood at 2,875 berri. Now with nails you need the four corners and typically two go in the center to prevent bending, but considering the dimensions of the small boards, five should be enough. So six nails per large board and five nails per small board, so 108 nails total. Nails are 50 berri for 100. Your notes say you still have some leftover nails, so one bag should be enough. So, that's 2,975 berri, round up to 3,000 for unforeseen expenses." Zoro recited as if reading from a script.

Usopp could only stare numbly. He wrote out everything Zoro had said, checked the math, and found it exactly as he'd said. Sure the only change Zoro had made to his original estimations were to use five nails instead of 6 on the small boards, a change which only saved 100 berri. But what was really impressive was that he'd done the multiplication so quickly. All in his head!

"Uh, Zoro."

"Mhm?"

"What's 17 times 5?"

"Huh?"

"17 times 5," Usopp repeated.

"85," Zoro instantly replied. "But what does that have to do with-"

"50 divided by 3."

"About 16 and a half, but what does this have to do with building expenses?" Zoro asked, his left eyebrow raised in confusion.

"Zoro,"

"Yeah?"

"Why are you so good at math?"

"Huh?"

"Why. Are. You. So. Good. At. Math?" Usopp enunciated.

"What are you talking about? I'm just answering your questions." Zoro flatly replied.

"But you're answering them really fast."

"I'm not doing anything special." Zoro replied with an annoyed growl. He stood up and left the bow, likely heading to a quieter place for his afternoon nap.

Meanwhile, Usopp handed his notes to Nami and headed to the galley for drink. Inside was Sanji, who was busy with the preparations for dinner.

"No sneaking food, Longnose." Sanji threatened, emphasizing with his knife, before turning back to the counter.

"I know," Usopp replied, holding his hands up to show how harmless his intentions were. He filled a glass with water and sat at the table, contemplating what had just transpired on the bow. Not that he ever considered Zoro to be a moron. But, there was a certain expectation to be had. It was like Luffy was spouting formulas on hydrodynamics, or if Nami were to not know a thing about geometry. Sure there was a possibility of it happening, but no one really expects it to!

Was it just him maybe? Was this kind of knowledge of math normal and he was just behind? Not that he'd ever considered himself to be slow or even stupid but…

"Hey Sanji?"

Usopp took the grunt as an acknowledgement of attention. "What's 17 times 5?" He chose the same problem he'd given to Zoro.

"Multiply it yourself, I'm busy." Sanji replied, dumping his chopped ingredients into a pan to simmer.

"Come on, just answer."

There was a brief pause, and the galley echoed with the sound of sizzling vegetables. After a few seconds, during which Usopp had assumed that Sanji was ignoring him, he heard, "85."

"And 50 divided by 3?"

"Is there a point to this Usopp?" Sanji snapped. "Because if this is some kind of game, go bother someone else."

"It's not, I'm just…comparing how quickly people answer."

"Why's that?" Sanji asked, checking on the bread baking in the oven.

"Well, while I was figuring out the building material budget, Zoro helped me out and-"

"That guy actually contributed for once?"

"And that's not the strange part. Turns out, Zoro's really good at math."

Sanji laughed once before turning away from the stove to face Usopp, as if to determine if what he said had been a joke. "The Marimo? Good at math? Yeah right, what's the real reason?"

"That's it. He answered the questions so fast but said it was no big deal. I was just wondering if everyone could answer that fast, but you just proved that wrong."

Sanji's cheerful grin fell to a threatening, level glare. "Are you saying I'm dumber than the plant?"

"No, no!" Usopp frantically replied. "Just because he can multiply and divide in his head faster than us, doesn't mean he's smarter."

"Us? So he's better at math than you too?"

Usopp nodded. "I don't know if his knowledge for math extends beyond multiplying and dividing, but at that level he's fast."

"Hm," Sanji hummed, turning back to the stove. "Well I guess last week makes sense then."

"Last week, what happened?"

"At the last island I took the Marimo shopping to pull the cart and he tells me to buy the more expensive barrel of apples because at the price per ounce it's cheaper." Sanji shrugged. "He was right, but I thought it was more of a lucky guess, or that maybe he hadn't noticed the price difference."

Usopp nodded in agreement. He set his glass in the sink and exited the galley. Perhaps after dinner he could try and see how much Zoro really knew…

Once the more stressful parts of dinner were over –namely, after Luffy ate and left the galley- Usopp remained seated as Zoro finished his sake. The galley was quiet with Chopper out on watch, Nami and Robin chatting quietly, and Sanji at the sink already beginning the long process of cleaning up.

"Hey Zoro," Usopp began.

"Hm," Zoro grunted.

"What's 15% of 70?"

"This again?" Zoro asked, turning to fix Usopp with an annoyed glare.

"Come on, just answer."

Zoro sighed. "10 and a half," he muttered before turning back to his sake.

"What's this about?" Nami asked, turning away from her yet to be finished dessert and her conversation with Robin.

"Zoro's really good at math so-"

"I'm not," Zoro protested without any real venom. "Usopp just keeps bothering me with questions."

"I didn't realize you had a hidden talent, Swordsman-san."

"It's not. I'm just answering his questions."

"So what's 15 squared?" Nami asked.

"225. Now would you quit bugging me with-"

"And the square root of 49?" Robin asked.

"7. This isn't that big of a deal."

"107 times 34,"

This time Zoro ignored Nami and took a long swig from his bottle.

"Oi, asshole, don't ignore Nami-swan!" Sanji reprimanded, aiming a kick at the side of Zoro's head.

Zoro ducked and growled unappreciatively. "Just do the math yourselves if you wanna know so bad!"

"We can't Swordsman-san, at least not as quickly as you."

Zoro huffed and drank, dodging another kick from Sanji for ignoring Robin this time. He lowered the bottle and shifted his attention to the dark haired archeologist. "I don't mind helping out, but rattling off questions and answers like this is just a waste of time."

"Yes, but it's an amusing way to spend the time at least." Robin replied with a relaxed grin.

"Maybe for you," Zoro scowled. He ran his hand through his hair and downed the rest of the bottle. "So you all really think it's so amazing that I can answer so fast?"

The chorus of yes –and one no from the sink of the kitchen- made Zoro's frown soften to a resigned smile. "Fine go ahead," Then he turned to Nami and answered, "3,638".

A/N: For those who would like an explanation, I created this headcanon during the Skypiea arc. After crashing from the sky, getting stabbed, and etc., Zoro adds 36+36+36 to get 108 by the time I've mentally carried the 1 to make 72. This was later reaffirmed in Water 7 when he says 108 x 2 is 216 without even thinking.

Zoro's reply, "because it's the answer" comes from an old conversation with one of my older brothers (with me filling Usopp's role). Basically my brother was having some trouble understanding that not everyone could multiply or divide so quickly in their head, especially if it involved decimal points. Ah, the blissful ignorance that comes with being a genius.

Also, this is my first time writing -in length- with Usopp, so feel free to let me know if I screwed it up and need to fix something.

Finally, the next post is likely to be small (in word count) as I have a double shift tomorrow. Just thought it'd be fair to give anyone who cared a heads-up.