## An Introduction to Probability

### Work Text:

March 2008

The other staff had long become accustomed to the fact that more noise came from Classroom 20 than any other. Not always - sometimes there was dead silence as the class listened, rapt, to the young teacher who had a strangely awe-inspiring presence for a skinny bloke in glasses - but more often than not lively debate flowed and eager voices clamoured to be heard, usually quelled eventually with a surprisingly thunderous bellow of ‘QUIET!’

On a damp morning in March, though, the atmosphere in Classroom 20 was oddly tense. “The stakes are high,” Harry reminded them. “There’s a few in the other classes that look promising, and I know how important this is to you all.”

Ismene Tallis, who spoke five languages and was rumoured to have already been wooed by magical and Muggle universities worldwide despite only being a fifth year, looked offended.

“Can’t we just get on with it?” someone at the back asked impatiently.

“All right,” said Harry, turning to the blackboard. “We’ve got the four categories -”

He broke off, because Samantha Nye’s hand had shot in the air. The Slytherin Seeker didn’t speak often, but when she did, it was usually because she’d spotted something no one else had.

“We need more information,” she said boldly. “I mean, take the date - has there been a pattern? It doesn’t make sense to just guess when there’s more to know.”

Harry nodded at her, pleased. “Good. That’s how you should be thinking. None of the other classes have asked me that, so far.” He picked up his chalk (he knew most teachers could make the writing just appear on the board with magic, but his handwriting was always much worse when he tried it) and spoke aloud as he wrote. “James was three weeks early, I think, and Al was bang on the due date …”

“What about hair colour?” Samantha pointed at the fourth category on the board, ‘HAIR - RED OR BLACK’. “Is it even possible for the baby to be red-haired?”

“How do you mean?”

“Well, you have to carry the gene, don’t you? Red hair is recessive. I know Mrs Potter has red hair, but you might not have the gene.”

Secretly Harry wondered if Weasley red hair was in fact recessive, as Weasley genes had a way of getting through, although both Al and James had black hair. “My mum had red hair,” he said.

Samantha wrote this down. He could see another student, a boy whose parents were teachers in a Muggle secondary school, drawing a table showing the probability of the baby being red- or black-haired. No one seemed to have any more questions, so he flicked his wand at the pile of parchment slips on his desk and sent it around the room until the whole class had one.

“OK,” he said. “You know how this works. One guess for each category - date, time, sex -” (several people sniggered) - “and hair colour. The person who gets all four - or is closest - gets a week off homework. So - place your bets.”

---

George, leafing through the parchment slips with an expression of great amusement, snorted and held one aloft. “Look at this. Lunchtime, 15th March, girl, black hair. Are they daft? It’s not going to be a girl!”

“That’s next week,” Harry said, panicking slightly. “We’ve not got everything yet.”

“I’m not having it next week, I’ve got book club,” said Ginny.

She was balancing a mug precariously on the summit of her immense stomach, protruding imperiously from her jumper like a monarch presiding over its subjects. It was so big Harry had started to think of it as a separate entity. Ginny hadn’t been amused when he’d set a place for it at the table.

“I don’t know why you’re so sure it’s not going to be a girl,” Ron said to George. “There are loads of girls in the family now.”

“Some of us are burdened with greater knowledge,” George said gravely. “ I don’t know why the prize is a week off homework.  You could’ve made loads of gold from this.”

“Strictly speaking,” said Harry, “I’m not supposed to take money from the students.”

Ginny prodded his shoulder. “What’s your bet, then?”

“Oh, er.” Harry tried to remember. “Boy, red hair … Two days early? I think I put the 29th of March. Oh, and three in the morning, I think.”

She twisted awkwardly to look at him. “You think it’ll be a boy?”

He did sort of (very much) hope that it would be a girl. He loved his sons beyond belief, but he would dearly love to have a daughter, even if the idea also terrified him. But he hadn’t written it down, just in case he jinxed it. He wasn’t, however, about to admit that, not when Hermione was in hearing distance.

It was strange to think that in a month’s time, probably, he would be a father of three and there would be another baby at Sunday dinners. He thought back to last Christmas, when there had been thirteen adults and nine children crammed into the Burrow, one of them being eight months pregnant Hermione, who had created a human traffic jam wherever she went. Now she was on one of the battered sofas with Hugo in her arms, looking very frazzled as she let out a rapid stream of concerns about things she might be doing wrong while poor Angelina, the unwilling recipient of the monologue, patted her on the arm and tried in vain to reassure her.

George carried on examining the wagers from Harry’s students. It had started out just amongst the seventh years, but word had spread and there was now a school-wide pool on the details of his third child’s birth. Even students he didn’t teach had come up to him and asked if they could transfer the week of no homework to another subject if they won. (He’d played it safe and said they’d better ask the teacher of said subject.) There was also a pool going in the staffroom, because Professor McGonagall had got extremely competitive and decided they ought to bet on the weight of the baby and precise time of birth as well. This one was for gold, which, it was gamely agreed, would in any case be used by the winner to buy a round at the Three Broomsticks.

“Can we bet on names?” George asked. “You’re running out of family ones for a boy, unless you plan on honouring Harry’s granddad, the esteemed Fleamont Potter -”

Harry closed his eyes briefly in shame. Discovering that he had a relative called Fleamont had been a humbling moment, and he’d felt especially bad about laughing with Ron when they’d heard that Draco Malfoy had named his son Scorpius Hyperion.

“I’ll let you use my name for the very reasonable price of five Galleons per annum,” said George.

“It’s not worth that, it’s only six letters,” said Ginny scathingly. “Anyway, you should pay us to use your name, I bet people would do all sorts to get Harry Potter to name his kid after them. We should put a competition in Witch Weekly.

George had opened the floodgates of inanity: fuelled by a glass or two of wine with dinner, everyone started shouting out suggestions, each more ridiculous than the last.

“Mundungus!”

“What about Kreacher? Or Buckbeak -”

“Ooh, Ginny dear, do you remember your great-great uncle Osbert? Or there’s Uncle Perry ...”

“Perry Potter!” Ginny interjected incredulously. “That’s worse than Buckbeak!”

“Ludo,” said Ron, who was counting them off on his fingers, “Peeves, Sir Cadogan, Severus, Stan, Gilderoy …”

“Good God,” said Harry quietly. Ginny threw him a look that said I’m sorry you had to marry into this and leaned forwards as much as she could to speak to James, who was trying to convince Al that biscuits were bad for him. Al’s gaze flickered uncertainly between the biscuit and his older brother, unsure whether or not to risk it.

“What do you think, Jimjam? What should we call the new baby?”

“FIREBOY,” said James.

There was a brief and rather bemused silence.

“Perry doesn’t sound so bad now, does it?” said George.

---

Ginny’s due date was the 31st of March, by which point they had agreed on names without the input of any of the Weasleys. Normal, human names, none of which belonged to anyone who had tried to kill them. As Ginny pointed out, you had to draw the line somewhere.

The 31st came - Harry spent the entire day at school with bated breath, waiting for the message he was sure would arrive at any moment - and went.

“Has it decided it’s not coming?” James asked, a little too hopefully.

Ginny’s bump was so enormous she looked as if she might burst at any moment; Harry, meanwhile, found himself facing increasing amounts of abuse upon his arrival at the castle every morning, as students and teachers alike crashed unceremoniously out of the birth date pool. “I can’t help it!” he protested, a bit alarmed by the intensity of the scowls he received in the staffroom.

“There are things you can do,” said Neville, waving a book at him. “Spicy food, pineapple, taking a walk -”

“Sex,” said Cordelia, the deputy headmistress, whom Harry thought of as a rather elegant grandmother figure - or had thought of, before she said that and traumatised him permanently.

“Don’t you go cheating your way to a win, Cordelia!” McGonagall warned sternly. “That baby will come when it’s good and ready!”

She had, Harry recalled with some amusement, predicted that it would be born ten days late. Ginny snorted when he told her this later. “What do you reckon she’d do if I went into labour now?” she wondered. “Spell my legs together and lock me in the dungeons?”

“Possibly,” Harry agreed. He eyed said legs thoughtfully. “You know, if you wanted to - I mean, it might be worth a try -”

“Oh yes?”

“I’m just thinking, you’re uncomfortable -”

“You’re such a gentleman,” said Ginny drily.

“I am,” said Harry. He glanced at her. “So …”

“Harry, I’m the size of a whale and these great mammoth things on my chest are killing me, we’re not having sex.”

---
McGonagall, a gracious winner, did treat all the staff to a round at the pub. Harry was befuddled from lack of sleep and couldn’t stop smiling like an idiot, especially when they all raised their glasses and toasted the newest Potter.

The winner of the student pool, earning a week off homework, was Gabe Hutchinson in the third year. “You’re always late, so I thought it might run in the family,” he told Harry cheekily, when Harry came in to introduce the new arrival to the staff and dropped by the Great Hall as well. “And I don’t really know anything about babies … it could have been a year late, for all I know.”

It had been twelve days late, actually, but Gabe - who had guessed fourteen - was closest. He’d also predicted that it would be born at nine in the morning (twenty-eight minutes past, though the contractions had started at four), with red hair.

George was so wrong on the name that no one bothered teasing him about it; besides, he’d been certain that it was a boy, and the baby with the most impressive set of lungs the midwitch said she’d ever heard - “just like Ginny,” Molly commented - was definitely a girl. A healthy sized baby girl, with wisps of flaming red hair and a scrunched up pink face and a great big loving family, aunts and uncles and cousins and brothers and two parents who couldn’t believe how lucky they were, to come home to.

“This is Lily,” Ginny said to Luna, who called in a week after Lily’s birth with beads in her hair and an unexpected husband in her wake. “Lily Luna.”

Luna’s large, pale eyes shone.

“Really? Do you really mean it?”

“We wanted a name that was special,” said Harry, feeling a bit choked up himself. “Special to us.”

---

In the hospital, little Lily finally having drifted off after a lot of screaming, Ginny lifted a hand to tenderly rest against Harry’s unshaven cheek and pulled him in for a soft kiss.

“I am really glad that we didn’t have to have six before we had a girl,” she said wearily. “My poor, poor mother. I’ll never be rude to her again.”