Algebrat
Someone who is annoyingly good at maths and who is always willing to give you the answer when you are working something out and correct your miscalculations when you are wrong.
"So 6 times 128, well 6 times 20 is 120...."
"It's 768"
"you can be a real algebrat you know that?"
"It's 768"
"you can be a real algebrat you know that?"