Blink. "Okay, how can maths be magic? I was pretty sure magic just—was."
"I don't know, I haven't taken it yet and Mum never did so she couldn't tell me about it."
"To find out what it's about. Besides, I have to take some things, I have explained my Divination opinion and don't have a reason to take Muggle Studies, and that leaves Runes and Arithmancy and maybe Creatures but I'll probably try for an independent study instead."
"Hmm... Well you've convinced me, guess I'll be taking those as well!"
"That's a lot of time. Maybe we'll have destroyed all Dementors and cured death and disease and fixed the House Elves problem if it needs fixing and restored Slytherin to its old glory and found everything out about thaumophysics by then."
"We'll see how that philosophy works for you, then, and I'll be the control group."