2011 AP Statistics Thread

[anotherindiankid]

my teacher told us not to worry about calculating power and Type II errors, but he said to know what each error was and be able to apply them in context

[birthbysleep]

Okay thanks! That's a relief.

[hellogoodbye893]

@anotherindiankid: what troubles do you have with binomial and geometric?

I get the gist of it being that binomial distribution has a mean of np (sample size times population proportion), standard deviation as sqrt(np(1-p)), and the pdf measures the probability of an exact number of trials.

Geometric probability should be used for questions that ask for the first time a success should occur.

[hellogoodbye893]

what's the difference between p-hat and p? (sample proportions)

[anotherindiankid]

yea i understand the calculations, but i don't know when to use which one. so, use geometric when they ask for the first time a success occurs? and when do you use binomials?

[anotherindiankid]

isnt p the parameter (for the population) and p hat the statistic (for the sample)?

[momomomo]

Geometric is when you do something UNTIL you get a success. Binomial is when you calculate the number of successes in a GIVEN number of trials.

Does that make sense?

[momomomo]

Can someone explain chi square vs chi square GOF? Like when to use them?

[hellogoodbye893]

from what i'm reading, parameters and statistics are synonymous to a measurement of a proportion? what i'm confused about is why they'd talk about p hat and then suddenly use p for finding mean and standard deviation for p hat

Here's an example that might help clear things up in binomial (i'm still confused about cdf!)

A manager notes that there is a .125 probability that any employee will arrive late for work. What is the probability that exactly one person is in a six person department will arrive late?

Note the key word: "exactly" one person

So...binompdf(n,p,x) -> binompdf(6,.125,1)= .385

[anotherindiankid]

ok i understand that

but i dont understand #26 and 27 on here: AP Statistics Practice Exam 2 | Education.com

like, i dont even know how to start

[momomomo]

the "c" stands for cumulative, so you used a PDF there because of the word "exactly"

[hellogoodbye893]

Can anyone tell me the difference between a sampling proportion and a sample mean?

[anotherindiankid]

yea a sampling proportion is x/n but a sample mean is when you're finding a specific value right? basically, it depends on what you want to find out i think. like if you want to find out the mean length of all fish, you would do a sample and find the sample mean. if you wanted to find out if cell phones or passengers distracted drivers more, you would find the proportions in the sample.

[anotherindiankid]

oh and sample mean is x bar, sample proportion is p hat
population mean is mu and pop. proportion is p

[momomomo]

Is there an answer key for that test anywhere? (for number 26 & 27)