For the most part, the basic magic education that Harry, Ron and Hermione go through in Hogwarts consists of the following subjects:- Defence Against the Dark Arts, Charms, Transfiguration, Potions and Herbology. Sure, there is a smattering of a few other subjects such as Care of Magical Creatures, Divinity, Arithmancy and so on.
Given this, wouldn't the logical conclusion be that Wizards and Witches from Hogwarts are unable to do Math??
I find this very disturbing. Since, it seems, wizards and witches only attend school beginning at age 11, it wouldn't be a stretch to suggest that they don't know simple algebra. Do they know how to compute something like 4 multiplied by 25? Say, if a customer comes into their shop and chooses to buy 5 Broomsticks or whatever at 85 galleons each, and receives 325 galleons from the customer, would the shopkeeper know that the customer is short by 100 galleons?
There doesn't seem to be a spell revealed just yet on how algebra and/or arithmetic is performed. Granted, there probably is not a real need for advanced stuff like Linear Algebra or Real Analysis, but some simple calculus might be worthwhile too. I mean, there are businesses in the wizarding world and businesses need some form of business model; most business models employ the use of calculus in their optimization process.
It boggles the mind, really. And sure, there are other really useful subjects that the magical world seems to forget. Languages, for example. Even basic Geography. I'd be surprised if a Wizard could point out where New Zealand is, assuming even basic general knowledge.
So, there you have it. Is the wizarding world really full of wizards and witches who, however powerful their wand work, are inept at even basic Mathematics? This really is a dark and difficult time.