Author's Note: Yeah, I was just looking back at my stories and then found a couple of mistakes. I've re-vamped it a little, but not too much. Just a couple of added/changed words, and a few corrected grammatical and spelling errors. Nothing too major, but I think it's a lot cleaner now. It's my most popular story to date, so I thought it'd pay to make it better. Enjoy. :))

Katekyo Hitman REBORN! and all related characters and events belong to Akira Amano.

Probability

(2011 Revised Edition) Reborn teaches Tsuna the mathematics of probability. Humor.

Tsuna stared at the advanced algebra book in front of him, trying to process all the numbers jumbled up in his brain.

There was something about the 'fundamental principle of counting in mathematics', and numbers with exclamation points after them.

Since when did numbers need exclamation points anyway?

Tsuna stared at the algebra book in front of him, trying to process all the numbers and punctuation marks jumbled up in his brain.

"Gah! I'm not getting any of this!"

"Baka Tsuna," Reborn muttered as he sipped on his espresso.

"This isn't as easy as it looks!" Tsuna retorted to the baby.

"Of course it is," Reborn scoffed. "Here's an example: if there are six sides on a die—"

"Die? Who's going to die—ow!"

And Tsuna rubbed at the sore spot on his forehead where the unidentified object Reborn threw hit him.

"'Die' as in the singular form of 'dice', you dumbass. That thing you throw when you play 'Snakes and Ladders'."

" . . . Oh."

"Moving on," Reborn said, putting down his espresso. "If there are six sides on a die, how often can you get a five?"

Tsuna held his hands out in front of him, seemingly counting something on his fingers.

"Could you repeat the question—OUCH! REBORN!"

"Baka Tsuna, you're completely hopeless. Here." Reborn reached up just as Leon transformed into a bright green die with white dots, the face with two dots replaced with the chameleon's eyes. Reborn lightly tossed the Leon-die to Tsuna, and the Vongola Decimo reached out to catch it.

And then the Leon-die slips through Tsuna's overly-loose grip.

"Dame Tsuna."

A bright red blush spread on Tsuna's face, and he bent over to pick up the fallen Leon-die, muttering a soft apology to the transformed chameleon.

"I will repeat the question," Reborn said. "If there are six sides on a die, how often can you get a five?"

Tsuna breathed in, repeating Reborn's question in his head: If there are six sides on a die, how often can you get a five?

Since there were six sides, with each side having a number between one and six, you should be able to get a five once out of every six throws, right?

" . . . One out of six?"

"Surprisingly enough, that's correct, Dame Tsuna."

Tsuna blinked his amber eyes, processing Reborn's words in his head.

" . . . Really?"

"Really."

A wide, sheepish grin erupted on Tsuna's face. He chuckled lightly to himself, feeling a sudden urge to shout out in joy (but that urge was immediately stomped down on by the thought of Reborn throwing something heavy at him again).

In any case, Sawada Tsunayoshi, age 14 and future boss of the Vongola Mafia Famiglia, felt like he had just won the lottery.

"Next question: If you have two coins, how often can you get two heads?"

A serious look appeared on Tsuna's face, and he grabbed a piece of a paper and a pencil, focusing really hard on solving the problem.

One coin had two sides—heads and tails. Since each coin had two possible outcomes, he should multiply the amount of possibilities of each coin with each other (he finally understood the fundamental principle of counting in mathematics!—always multiply the amount of possible outcomes for every variable to get the total amount of possible outcomes) to get the total amount of possibilities, a number which would function as the denominator of the fractional value.

Two times two was four. That meant that for every four throws, the probability of getting two heads was—

Wait, if you threw the two coins, you can get two heads, two tails, a tail and a head, or a head and a tail—those were the four possibilities. Two heads was one of those possibilities. That meant that the possibility of getting two heads with two coins was once out of every four throws.

"One out of four!"

"Correct."

A wide grin broke out onto Tsuna's face once again as he energetically punched the air in front of him in success (but made sure he didn't make any noise in fear that Reborn would throw something heavy at him again).

"Next question: There were originally five candidates to become the next Vongola boss. Three of them were killed. Xanxus isn't eligible. You're the last one. What's the possibility of your becoming Vongola Decimo?"

Tsuna grinned at Reborn, finding the last question particularly easy. Since three were killed, of course they couldn't become boss. If Xanxus wasn't eligible, then that left him as the last possible successor.

"One hundred percent, of course!" Tsuna exclaimed, knowing full well in his heart that he had the right answer. It was the first time he'd ever been so sure about the answer to any math question.

Reborn smirked as he picked up his espresso cup. "Correct again, Dame Tsuna. I'm glad you've finally accepted your position as Vongola Decimo.

Tsuna kept grinning for a full ten seconds before he finally realized what the Arcobaleno had just made him admit. The ecstasy he felt about getting a math question correct had blinded and deafened him.

"REBORN! I'M NOT BECOMING A MAFIA BOSS!"

"You said the possibility of you becoming the next boss was one hun—"

"YOU TRICKED ME INTO SAYING THAT! GAH! I CAN'T BELIEVE I FELL FOR IT!" Tsuna screeched, pulling at his spiky hair and knowing full well in the back of his mind that Reborn would be recalling to this event in times to come.

"Numbers don't lie," Reborn stated plainly.

"I'M NEVER GOING TO ASK FOR YOUR HELP IN MATH AGAIN!"