normalpdf/normalcdf on GDC

[haris_87]

We have the SL exam in a few days....and I was looking over my GDC and I dont quite get the difference between normapdf/normalcdf and binompdf/biompdf. I always get confused between the four, so which one do we for what type of question (could you also please give an example...).

Any other HELPFUL tips to prepare for the exam.

PS it's TI-84 Silver Edition

Edited April 28, 2012 by Summer Glau
please don't use text speak.

[Jyrgen]

(Assuming you mean the TI84+)

Binompdf and binomcdf: both used for binomial distribution

pdf: when you want to know the probability that the event happens exactly the amount of x you specify.

cdf: when you want to know the probability that the event happens less than the amount of x you specify. For example, you want to get the chance that at least ten events happen? Use

1 - P(X<10)

= 1 - binomcdf(trials,probability,10)

And normalcdf is your primary tool in solving normal distribution problems. It works like binomcdf, except that

1) it can also specify a lower limit so you get P(lower < Z< upper value)

2) never use normalcdf when solving problems that are not specificially about normal distribution, and never use binompdf/cdf for normal distribution problems.

ignore normalpdf

I would suggest getting the latest OS update for the calculator from the manufacturer's website, it may improve the easiness of using the thing immensely

Edited April 28, 2012 by Jyrgen

[Eastcoast93]

Also it may be obvious but invnorm is another function you may need. It is required for normal distribution problems where the area/probability is given and you are working out certain boundaries.

[Michel Tabari]

I would suggest doing it manually using the values found in the data booklet. At times my calculator has given me values for the normal distribution and inverse probabilities that are too far off from the correct answer.

[Jyrgen]

I would suggest doing it manually using the values found in the data booklet. At times my calculator has given me values for the normal distribution and inverse probabilities that are too far off from the correct answer.

Haven't experienced this, but would like to point out that Paper 2 questions can actually ask values not found in the booklet (the lowest p value given in the booklet is 0.50). Thus you have to learn to operate your calculator.

[DeBrogliez]

(Assuming you mean the TI84+)

Binompdf and binomcdf: both used for binomial distribution

pdf: when you want to know the probability that the event happens exactly the amount of x you specify.

cdf: when you want to know the probability that the event happens less than the amount of x you specify. For example, you want to get the chance that at least ten events happen? Use

1 - P(X<10)

= 1 - binomcdf(trials,probability,10)

I think you have done a mistake here!

Since you want to find the chance of at least 10 events happen

Then you should include 10 itself

So the answer is

= 1 - binomcdf(trials,probability,9)

[Michel Tabari]

I would suggest doing it manually using the values found in the data booklet. At times my calculator has given me values for the normal distribution and inverse probabilities that are too far off from the correct answer.

Haven't experienced this, but would like to point out that Paper 2 questions can actually ask values not found in the booklet (the lowest p value given in the booklet is 0.50). Thus you have to learn to operate your calculator.

Actually, by the symmetry of the inverse probability graph you can find the inverse probabilities for values less than 0.50 manually, using the data booklet. But I get your point.

Edited April 29, 2012 by Michel Tabari

[Jyrgen]

(Assuming you mean the TI84+)

Binompdf and binomcdf: both used for binomial distribution

pdf: when you want to know the probability that the event happens exactly the amount of x you specify.

cdf: when you want to know the probability that the event happens less than the amount of x you specify. For example, you want to get the chance that at least ten events happen? Use

1 - P(X<10)

= 1 - binomcdf(trials,probability,10)

I think you have done a mistake here!

Since you want to find the chance of at least 10 events happen

Then you should include 10 itself

So the answer is

= 1 - binomcdf(trials,probability,9)

Oh that's correct, a very basic mistake from my part. Thanks.

I would suggest doing it manually using the values found in the data booklet. At times my calculator has given me values for the normal distribution and inverse probabilities that are too far off from the correct answer.

Haven't experienced this, but would like to point out that Paper 2 questions can actually ask values not found in the booklet (the lowest p value given in the booklet is 0.50). Thus you have to learn to operate your calculator.

Actually, by the symmetry of the inverse probability graph you can find the inverse probabilities for values less than 0.50 manually, using the data booklet. But I get your point.

Didn't cross my mind, thanks. Then it should be supposed that Paper 1 questions could ask for values < 0.50 too.

[dessskris]

is the CDF one less than and equal to, or just less than?? thanks!

[IB>mindf**k]

is the CDF one less than and equal to, or just less than?? thanks!

Depends,

if p(x<=s) then you do binomcdf(n,p,s)

if p(x<s) then binomcdf(n,p,s-1)

if p(x>s) then 1-binomcdf(n,p,s-1)

if p(x=>s) then 1-binomcdf(n,p,s-1)

where n is nr of trials, p is probability of success

I hope this helps; everyone good luck with exams

Edited May 2, 2012 by IB>mindf**k

[Guest]

...so this may be an incredibly dumb question considering Paper 1 is tomorrow, but we've never used binompdf or binomcdf in class - we only ever used normalpdf/cdf... am I completely screwed?

[IB>mindf**k]

...so this may be an incredibly dumb question considering Paper 1 is tomorrow, but we've never used binompdf or binomcdf in class - we only ever used normalpdf/cdf... am I completely screwed?

No, i assume that as you haven´t learnt how to get binomial probability using gdc, you can do it by hand (using formulas in data booklet) hence you understand the theory and such behind it, so just learn how to use gdc on such questions by heart by doing as many binomial probability questions you got in your book using gdc now