# Calculator problems (Casio fx-9750GII

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Hi everyone,

I've been having problems with the answers coming out my GDC, specifically the Casio fx-9750GII.

1) The linear regression equations it calculates (ax+b) from data sets are always subtly different to what appears in the mark scheme. I've tried using a+bx and fiddling with the settings, but nothing seems to change them.

2) When trying to use grouped frequency data in the stats mode, it often outputs incorrect information for standard deviation and things like that.

3) The nCd and nPd results are sometimes a little different, although I might just be using them wrong- how do I know when to use which one?

Any advice? It's a bit nervewracking not being able to trust my calculator this close too the exam.

Thanks very much

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Hi!

I don't know about 1) and 2) (I think they are not in the HL syllabus).

Is NCD and NPD the normal distribution functions?  (or are you talking about the permutations/combinations nCr and nPr?)

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Yeah I think they're what you call the normal distribution functions! The ones where you add uppers and lowers and the mean and standard dev

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@eross You are right linear regression is in SL and the HL stat/prob optional topic, but not in HL core. But you should know about grouped frequency data for HL. This is HL topic 5.1
@farmerjoe I do have your calculator model but I didn't use it in my exams.
To do grouped variables, you want List1 to be all the median values of the interval. Eg number from the interval 20 to 30, you want to enter 25 in List1.
In List2 enter the corresponding frequencies.
F2 (CALC), then F6(SET), and set
1Var XList to List1, and
1Var Freq to List2.

Finally, you do not want to use Npd (or NormPD) because that's the value returned by the normal function. not the area under the curve.
For Ncd, the syntax is (lower bound, upper bound, standard deviation, mean). Ncd calculates the area underneath the curve between your lower and upper bound, which is the probability.

Edited by kw0573

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