Guide to Probability Notation

[Greatness]

Would VCAA give us a solve for n question on exam 1? - The calculations would have to pretty simple tho...

[luken93]

Would VCAA give us a solve for n question on exam 1? - The calculations would have to pretty simple tho...

Yeah I would doubt it, but if they did I can't imagine it being more than a Pr(X >= 1) = ...., to keep the calcs relatively simple..

[tony3272]

They did last year, which was the only mark i lost on that exam.... You had to use trial and error for it though.

[yabbaboo]

Um, are we allowed to write this whole thing down on the paper, eg normcdf(60, 95, 60, 15)? I always wrote like that on my sacs and I never lost marks for that.

[b^3]

Um, are we allowed to write this whole thing down on the paper, eg normcdf(60, 95, 60, 15)? I always wrote like that on my sacs and I never lost marks for that.

Thats calculator syntax, I don't think you would lose marks for writing it, you just wouldn't get the marks for writing the X~(60,0.2). VCAA are always  stating in the assesment reports to not write caclulator syntax.

Remember that with sacs, your teachers may be marking a slightly different way to VCAA.

Just a quesition guys, what do we write when we have the inversnorm function?
i.e. Binomial X~(n,p)
Normal distributions X~(u,o^2)
inversnor X~"_"(u,o^2)

[mjwalka]

Good post, I've never really got a clue to write for most of prob. I think this might find it's way on my bound reference haha.

[b^3]

EDIT2: NVM I'm blind.

[AleksIlia]

Hey, I never really got the difference between normpdf vs normcdf on the CAS, I don't get why you can plug in a specific value because I thought as all normal distributions are continuous the probabiltu at a given point is zero. Can someone explain? :S

[Greatness]

if you want Pr(X>2) then you're going from 2 to inf which is why there is the upper and lower for CDF but if you want it for a particular value you just use PDF.
You have to remember that the normal bell curve extends to infinity.

[AleksIlia]

if you want Pr(X>2) then you're going from 2 to inf which is why there is the upper and lower for CDF but if you want it for a particular value you just use PDF.
You have to remember that the normal bell curve extends to infinity.

But how do you find Pr(X=2) for a normal distribution if Pr(X=x) is 0 for a specific value of x

[b^3]

pdf is from negative infintiy to the value you specify where as cfd is between the two values you specify.

[AleksIlia]

Oh, I see then, but if I put in the normal distribution mean 0 sd 1 for x value of 0 I don't get 0.5?

[b^3]

Oh, I see then, but if I put in the normal distribution mean 0 sd 1 for x value of 0 I don't get 0.5?

Wait, you're right I may be wrong let me just check.

[b^3]

Ok got it. The pdf function gives the height of the normal (ow whichever you use) at the point of the function.

Sorry for the confusion. But in a continuous function we can't have that so I don't know why it is there.

EDIT: sometimes we get a question like the example in the first post, test scores (where you can't have half a mark) so this will allow you to calculate the probability of say 65 /100 or 69/100.

[AleksIlia]

Okay thanks! Also thanks for those CAS guides, super helpful. Good luck Tuesday