192 replies to this topic

[BeefontheBone]

Do you choose particular subjects to study for the HSC then? Because that question would be very easy for a dedicated maths course at age 18, but probably about right for a compulsory maths element of a more general course.

[Iron_Scarecrow]

Math was compulsory up until about 2 or 3 years ago. 2 unit is what most of the state would do, there is 3 unit which is a lot more complex and then there 4 unit, even more complex.

I did 3 unit in year 11 but my laziness really messed me up. My math teacher always said I have the mind and potential to be a good mathematician but I'm just too damn lazy. Of course he used different phrasing but that was the point he was trying to make.

And this HSC is the NSW education system every state of australia has a different system and its get confusing.

Edited by Iron_Scarecrow, 25 November 2005 - 01:42 PM.

[seer]

Heh! I don't even have math in school...

[A. J. Raffles]

seer, on Nov 26 2005, 10:44 PM, said:

Heh! I don't even have math in school...

You don't? How odd.

[Iron_Scarecrow]

BeefontheBone, on Nov 26 2005, 12:03 AM, said:

Do you choose particular subjects to study for the HSC then? Because that question would be very easy for a dedicated maths course at age 18, but probably about right for a compulsory maths element of a more general course.

And yes you pick your own subjects for years 11 and 12. English is compulsory, and then you pick everything else, most people pick maths anyway. To pass the HSC you have to have at least 10 units which is basically 5 subjects, each one being 2 units. Although you could do 3 unit english, 4 unit maths and 3 unit history and pass, but that would be a lot of work.

[A. J. Raffles]

This is only very vaguely maths-related, but does anyone happen to know how the last number in an ISBN code is calculated? That's been puzzling me for ages now.

[BeefontheBone]

Actually I did know this - I *think* it's the weighted sum of the previous digits mod 11, as a check digit to ensure the ISBN is valid. I'll check. *checks* Yup, I was right.

The first digit is (apparently) the language, the second and third are for publisher, digits 4 to 9 the book (these almost certainly vary around the world - for a start there are more than 10 languages in which books are published) and the 10th is the check digit, the inclusion of which allows the code to detect (though not correct) any single-digit error and any double-digit error where two digits are interchanged (transposition errors).

The check digit is indeed the weighted sum of the previous 9 digits calculated modulo 11 (i.e. it's the sum over i running from 1 to 9 of the terms i*d(i) where d(i) is the i-th digit). The Xs in ISBNs are treated as having value 10, since the ISBN code is based on the field Z11, the integers {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, X} with addition and multiplication calculated modulo 11.

To pluck an example off my bookshelf, the ISBN on Douglas Adams and John Lloyd's The Deeper Meaning of Liff is 0-330-32220-6: it's in English, published by Pan, and has check digit 6, which is equal (mod 11) to (1*0) + (2*3) + (3*3) + (4*0) + (5*3)+ (6*2) + (7*2) + (8*2) + (9*0)
(this sum comes to 72, which is indeed 6 mod 11).

Incidentally, it is maths-related - at least, I learned this in a Coding Theory course
As an exercise for anyone who fancies it, prove that the code can detect any single-digit error and any two-digit error caused by transposition.

[DannyMc252]

Uhm, sort off on-topic to the slightly off topic stuff...
Whats an ISBN code?

[Qbix]

it's an "unique" number they put on books.

[Havell]

Not unique for every single book, you understand, but unique for every publication (it's not just books y'see, but other published stuff).

[A. J. Raffles]

R Havell, on Nov 30 2005, 09:34 PM, said:

Not unique for every single book, you understand, but unique for every publication (it's not just books y'see, but other published stuff).

Hmm, but ISBN stands for International Standard Book Number, so I'd assume it is restricted to books.

I knew about the meaning of the other digits (I've worked at a bookshop for several years), but I never could figure out how you can actually use the check digit to checks whether the other digits are printed correctly. (Obviously those scanner thingies do that for you.) Anyway, thanks, Beef.

[Tom Henrik]

A.J. working in a bookstore... who would've thought it

[MdaG]

This is fun. In particular project Euler.