• Congratulations to the Class of 2024 on your results!
    Let us know how you went here
    Got a question about your uni preferences? Ask us here

Statistics Marathon & Questions (5 Viewers)

davidgoes4wce

Well-Known Member
Joined
Jun 29, 2014
Messages
1,877
Location
Sydney, New South Wales
Gender
Male
HSC
N/A
Re: University Statistics Discussion Marathon

Statistical validity refers to whether a statistical study is able to draw conclusions that are in agreement with statistical and scientific laws. This means if a conclusion is drawn from a given data set after experimentation, it is said to be scientifically valid if the conclusion drawn from the experiment is scientific and relies on mathematical and statistical laws.

id also refer out C, and would go for B in this question.
 

Flop21

Well-Known Member
Joined
May 12, 2013
Messages
2,807
Gender
Female
HSC
2015
Re: Statistics

is there an easy way to find the probability mass function??

right now im just looking at example P(X=x) like P(X=1... etc.) and trying to find a pattern

but this is hard for tricky ones
 

He-Mann

Vexed?
Joined
Sep 18, 2016
Messages
278
Location
Antartica
Gender
Male
HSC
N/A
Re: Statistics

is there an easy way to find the probability mass function??

right now im just looking at example P(X=x) like P(X=1... etc.) and trying to find a pattern

but this is hard for tricky ones
Got an example question?
 

Flop21

Well-Known Member
Joined
May 12, 2013
Messages
2,807
Gender
Female
HSC
2015
Re: Statistics

Got an example question?
A box contains four red and two black balls. Two balls are drawn. Let X be
the number of red balls obtained. Find fX(x)


Okay so if I haven't screwed up, P(X=0) = 1/15, P(X=1) = 4/5, P(X=2) = 2/5, and any other value of X, P = 0.

So how do I put this into a proper answer for this question?
 

InteGrand

Well-Known Member
Joined
Dec 11, 2014
Messages
6,109
Gender
Male
HSC
N/A
Re: Statistics

A box contains four red and two black balls. Two balls are drawn. Let X be
the number of red balls obtained. Find fX(x)


Okay so if I haven't screwed up, P(X=0) = 1/15, P(X=1) = 4/5, P(X=2) = 2/5, and any other value of X, P = 0.

So how do I put this into a proper answer for this question?










 

Flop21

Well-Known Member
Joined
May 12, 2013
Messages
2,807
Gender
Female
HSC
2015
Re: Statistics

yeah whoops typo'd something in my calculations so that stuffed up,

so your final sentence, is that enough for an answer or do I need to know how to put it in a form with x ?
 

InteGrand

Well-Known Member
Joined
Dec 11, 2014
Messages
6,109
Gender
Male
HSC
N/A
Re: Statistics

yeah whoops typo'd something in my calculations so that stuffed up,

so your final sentence, is that enough for an answer or do I need to know how to put it in a form with x ?
 

Flop21

Well-Known Member
Joined
May 12, 2013
Messages
2,807
Gender
Female
HSC
2015
Re: Statistics

extremely helpful thanks!
 

Flop21

Well-Known Member
Joined
May 12, 2013
Messages
2,807
Gender
Female
HSC
2015
Re: Statistics

I have notes saying if X is discrete, cdf is SUM t<=x fX(t)

I might not be looking hard enough but I cannot find examples of this being used anywhere,

say we are given:

fX(x) = P(X = x) = p(1 − p)^x, x = 0, 1, 2, . . . ; 0 < p < 1

how do I calculate the FX(x) = P(X <= x)?

Or to start me off, how do I use what I'm given in the formula? Thanks.
 

InteGrand

Well-Known Member
Joined
Dec 11, 2014
Messages
6,109
Gender
Male
HSC
N/A
Re: Statistics

I have notes saying if X is discrete, cdf is SUM t<=x fX(t)

I might not be looking hard enough but I cannot find examples of this being used anywhere,

say we are given:

fX(x) = P(X = x) = p(1 − p)^x, x = 0, 1, 2, . . . ; 0 < p < 1

how do I calculate the FX(x) = P(X <= x)?

Or to start me off, how do I use what I'm given in the formula? Thanks.






 

Flop21

Well-Known Member
Joined
May 12, 2013
Messages
2,807
Gender
Female
HSC
2015
Re: Statistics

Given the diameter of a trunk fX(x) = 1, 0 < x < 1

I found that the E(X) = 0.5

How do I find the E(X) of the area of the trunk?

I tried doing it this way, area = Pi*r^2, so Pi*(d/2)^2, then I went so d = 1, make LHS = Pi*(d/2)^2 and then you get RHS = Pi/4 which is the area fX(x).

Then I found the E(X) of this, and got Pi/2, which is incorrect.

The correct answer is Pi/12, since they get area = Pi/4 * X^2, and E(A) = Pi/4*E(X^2).

So how did they get that Pi/4 * X^2?
 

InteGrand

Well-Known Member
Joined
Dec 11, 2014
Messages
6,109
Gender
Male
HSC
N/A
Re: Statistics

Given the diameter of a trunk fX(x) = 1, 0 < x < 1

I found that the E(X) = 0.5

How do I find the E(X) of the area of the trunk?

I tried doing it this way, area = Pi*r^2, so Pi*(d/2)^2, then I went so d = 1, make LHS = Pi*(d/2)^2 and then you get RHS = Pi/4 which is the area fX(x).

Then I found the E(X) of this, and got Pi/2, which is incorrect.

The correct answer is Pi/12, since they get area = Pi/4 * X^2, and E(A) = Pi/4*E(X^2).

So how did they get that Pi/4 * X^2?






 
Last edited:

Users Who Are Viewing This Thread (Users: 0, Guests: 5)

Top