# STEP II statistics topic notes - small typo

Hello,

Just to report a minor typo in STEP II Statistics topic notes : The Poisson distribution (page 2) defines P( X = r ) = f(n) instead of f(r)

Hope this helps !

### Thanks!

Corrected now. Thanks for pointing it out!

### You're welcome !

Well, you're welcome ! Another typo in STEP II Miscellaneous may be the equation of the circle of radius R passing through $(a,b)$. I may be mistaken, but if the circle (eg the curved line) passes through $(a,b)$, we can't have the equation as there are an infinite number of circle of radius R passing through (a,b). In the equation given, $(a,b)$ is the centre.

Also, something I'm not quite sure about is the expansion of $(1 + x)^k$. We don't need $abs(x) < 1$, do we ? The latter condition is only required if we want to approximate $(1 + x)^k$ by the first terms of the expansion.

### Edit

Well, in fact, now I've understood the meaning of the binomial expansion. Sorry !

However, in the correction of STEP II miscellaneous Q7 (2007 S2 Q1), there is one too many $4$ in the approximation of $\sqrt{6}$ : $\sqrt{6} \approx 2.44949$ and not $\sqrt{6} \approx 2.444949$.
Anyway, thank you for being so helpful, and hope this helps.

Yep, agreed!

### Which question?

For the typo about a circle, I am assuming that this is from the solutions document? If so, which question is it please? (I have had a quick scan through and cannot find it!).

Thanks for all the help :-)

Oops, sorry I forgot to mention it was in the topic notes (here)

### Thanks

That was an odd mistake to make, sorry!

### Mistakes corrected

Thanks again!

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