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**zetafunc.****Guest**

Unlike adriana my performance in STEP won't affect whether or not I go to UCL, but realistically I think I will get at least S, 1 and 2 in STEP I, II and III. I would like to get 3 S-grades, but that will take some more work. It is very difficult to get an S in STEP III.

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 92,385

66 days away you say? That is plenty of time.

**In mathematics, you don't understand things. You just get used to them.**

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**zetafunc.****Guest**

Yes -- although it is hard to complete a whole paper in one day...

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 92,385

If I can help just post it.

**In mathematics, you don't understand things. You just get used to them.**

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**zetafunc.****Guest**

It is OK at the moment, for 2004-2012 they provided solutions -- although for 2003 and beyond they didn't include them.

adriana says she will aim to do 6-8 questions on the weekends, which is pretty good.

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 92,385

That may be your opportunity. Do not volunteer, let her ask.

**In mathematics, you don't understand things. You just get used to them.**

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**zetafunc.****Guest**

Sometimes she asks for help, sometimes we do a question together. She needed help on a geometry question and I couldn't help her with it because it puzzled me too.

Some of these questions can be really annoying, requiring tedious amounts of algebra...

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 92,385

That is what a CAS is for.

**In mathematics, you don't understand things. You just get used to them.**

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**zetafunc.****Guest**

It would be nice to use one, but not for this exam, it is not permitted. No calculators. In fact I heard they ban measuring instruments/compasses/etc. too. Pen and paper.

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 92,385

I meant for checking right now.

**In mathematics, you don't understand things. You just get used to them.**

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**zetafunc.****Guest**

They provide solutions thankfully, so no need to use them for STEP. I use them occasionally though but only for simple things like pattern-spotting, like when you got me to work out the co-efficient of x[sup]n[/sup] in the expansion of (1 + x + x[sup]2[/sup] + ... )[sup]k[/sup], which was (n + k - 1) C (k - 1). That one has been very useful.

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 92,385

Yes, that was a good problem.

**In mathematics, you don't understand things. You just get used to them.**

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**zetafunc.****Guest**

Also, if G(x) is some generating function, is it always true that

G'(1) = E(X), and that

G''(1) + G'(1) - (E(X))^2 = Var(X)?

So for instance, the PGF for a simple 6-sided, fair die:

would this kind of thing work?

**zetafunc.****Guest**

The last bit of LaTeX should be differentiating the GF, setting equal to 1, and getting 3.5, the correct answer.

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 92,385

Yes, you can get all the moments from the generating function.

**In mathematics, you don't understand things. You just get used to them.**

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**zetafunc.****Guest**

Do the moments have any meaning for non-probability GFs? Combinatorial problems for instance?

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 92,385

I do not think so, A probability GF is different.

**In mathematics, you don't understand things. You just get used to them.**

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**zetafunc.****Guest**

Oh, okay. STEP III has some generating function questions, I didn't know they came up in STEP.

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 92,385

They are slowly working their way into every level of mathematics.

**In mathematics, you don't understand things. You just get used to them.**

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**zetafunc.****Guest**

adriana doesn't seem to get them at all unfortunately... maybe it is the way I am explaining it.

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 92,385

They can be a bit difficult to get at first but once you do...

**In mathematics, you don't understand things. You just get used to them.**

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**zetafunc.****Guest**

I found them difficult at first too, I still find them a bit tricky, they are very powerful though.

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 92,385

They are a lot of fun too.

**In mathematics, you don't understand things. You just get used to them.**

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**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,822

Speaking og GFs, bobbym, have you been able to get through the 3rd chapter of GFology?

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

The knowledge of some things as a function of age is a delta function.

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 92,385

Absolutely not, it is said Wilf could not get through it.

**In mathematics, you don't understand things. You just get used to them.**

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