STAT267: Good at statistics? Want to help with a homework question?

aeradyn · 02-14-2006, 02:22 PM

I need help.

----
The Rockwell hardness index for steel is determined by pressing a diamond point into the steel and measuring the depth of penetration. We wish to test, with a level of significance of 5%, the null hypothesis that the mean Rockwell index for a certain type of steel is is 75.0 versus the alternative hypothesis that it is not equal to 75.0. For 30 specimens of a this type of steel, the Rockwell hardness index averaged 72.5 with a standard deviation of 8.20. What is the p-value for this test. State your answer to 3 places of decimal.
----

Ok so:
α = 0.05
Ho: µ= 75.0
Ha: µ != 75.0
n = 30

for the sample measured:
_
x = 72.5
σ = 8.20

I am working on it on my own right now. I am having a hard time.

aeradyn · 02-14-2006, 02:32 PM

Ah got it I think.

0.0969?

Scorpvenom · 02-15-2006, 12:14 PM

I think you are wrong.

You have your null and alternative hypothesis setup correctly assuming that != means not equal to. The standard deviation should be s and not sigma, but it doesn't really matter how you identify it as long as you plug it into the formula correctly.

First, you need to realize that this is a two sided test (due to the fact that your alternative is not equal to), so you want the two tail areas, which are basically symmetric.

Find your test statistic either using a z or t distribution, I prefer t, but it shouldn't really matter given the large sample size.

T.S. = x bar - mu / (s or sigma / sqr rt of n) I got 22.40

Then using a t or z distribution (doesn't really matter since your n is 30) you get an extremely small p value. I don't have minitab or another program to know the exact p value but an answer of p-val < .01 should be fine.

You reject the null hypothesis (Ho). From this data, we are 95% confident (or confident at the 5% level of significance) that the mean Rockwell index for a certain type of steal is different than 75 on average in the population. It appears from the data that the mean average in the population is smaller than 75.

BruuceWarduck · 02-15-2006, 12:17 PM

i got 33.062

Blaezenfury · 02-15-2006, 12:20 PM

what kind of steel are we talking about?

HRPO?
CR?
flat bar?

are you just trying to determine the gauge of the steel? or how much preasure it can take?

Samus Aran · 02-15-2006, 01:39 PM

Quote:

Originally Posted by Blaezenfury

what kind of steel are we talking about?

HRPO?
CR?
flat bar?

are you just trying to determine the gauge of the steel? or how much preasure it can take?

Oh God I can't tell if you're serious or not.

Anyways I did a Z-test an got a p of .094942. I'm not sure if that's the correct test to do since it's been a while.

Samus Aran · 02-15-2006, 02:13 PM

Quote:

Originally Posted by Blaezenfury

what kind of steel are we talking about?

HRPO?
CR?
flat bar?

are you just trying to determine the gauge of the steel? or how much preasure it can take?

Life > Statistics > Tom Cruise > Blaezen

Blaezenfury · 02-15-2006, 03:18 PM

I was being serious potam.

coffee shut your retarded face, douchebag.

GrobbeeTrull · 02-15-2006, 04:14 PM

Blaezen, the type of steel doesn't matter, because we're not trying to find the type of steel. We're trying to determine STATISTICS.

Blaezenfury · 02-15-2006, 05:54 PM

the type of steel OBVIOUSLY FUCKING DETERMINES ITS STATISTICS YOU FUCKING IMBECILE.

hi different types of steels are made differently, meaning different chemicles and or different process of making it. HRPO = hot rolled pickled & Oiled. CR = Cold Rolled. etc..

What the fuck kind of retard are you? DURRR THE TYPE OF BREAD DOESENT DETERMIN ITS CALORIES/SODIUM/CARBS! HAW HAW DURR.

seriously you stupid cunt, dont ever fucking put your mouth where it doesen't belong. it'll get your ass owned.

Ibliss · 02-15-2006, 07:13 PM

Dude, seriously...its a fucking stat problem. It really doesnt matter what kind of steel they are describing. They could be talking about Jello and it wouldnt matter.

Duppin · 02-15-2006, 08:33 PM

My god.

This thread really drives home why people make fun of Blaezenfury.

I have never seen more determined ignorance in my life.

GrobbeeTrull · 02-15-2006, 09:13 PM

Quote:

Originally Posted by Blaezenfury

the type of steel OBVIOUSLY FUCKING DETERMINES ITS STATISTICS YOU FUCKING IMBECILE.

hi different types of steels are made differently, meaning different chemicles and or different process of making it. HRPO = hot rolled pickled & Oiled. CR = Cold Rolled. etc..

What the fuck kind of retard are you? DURRR THE TYPE OF BREAD DOESENT DETERMIN ITS CALORIES/SODIUM/CARBS! HAW HAW DURR.

seriously you stupid cunt, dont ever fucking put your mouth where it doesen't belong. it'll get your ass owned.

Ok cuntbubble, lemme lay it out for you:

Quote:

We wish to test, with a level of significance of 5%, the null hypothesis that the mean Rockwell index for a certain type of steel is is 75.0 versus

Bolded are the important parts. Notice, they dont give a flying fuck which steel it is. You know why? BECAUSE THEY ALREADY HAVE ROCKWELL INDEXES FOR THE STEEL. They're trying to find the AVERAGE of it, given a set of parameters.

Quote:

For 30 specimens of a this type of steel, the Rockwell hardness index averaged 72.5 with a standard deviation of 8.20. What is the p-value for this test.

Hi, it doesn't fucking matter, because guess what, the 30 specimens all came relatively close to one another. The number could be 4, the number could be 200, IT DOESNT MATTER ONE FUCKING BIT WHAT TYPE OF STEEL IT IS BECAUSE ITS NOT THE IMPORTANT PART.

Maybe try high school again, or perhaps community college?

Eomer · 02-16-2006, 08:09 AM

Intentional or not, Blaezen ought to go down in internet history as one of the most effective trolls of all time.

Belefuu · 02-16-2006, 09:30 AM

Well if it's not intentional, then he wouldn't be a troll now would he? He would just be a retard.

I think we're all pretty sure it's not intentional.

02-14-2006, 02:22 PM	#1 (permalink)
aeradyn doesn't get it Join Date: Apr 2003 Location: Canada Posts: 130 +0 Internets	STAT267: Good at statistics? Want to help with a homework question? I need help. ---- The Rockwell hardness index for steel is determined by pressing a diamond point into the steel and measuring the depth of penetration. We wish to test, with a level of significance of 5%, the null hypothesis that the mean Rockwell index for a certain type of steel is is 75.0 versus the alternative hypothesis that it is not equal to 75.0. For 30 specimens of a this type of steel, the Rockwell hardness index averaged 72.5 with a standard deviation of 8.20. What is the p-value for this test. State your answer to 3 places of decimal. ---- Ok so: α = 0.05 Ho: µ= 75.0 Ha: µ != 75.0 n = 30 for the sample measured: _ x = 72.5 σ = 8.20 I am working on it on my own right now. I am having a hard time.

02-15-2006, 12:14 PM	#3 (permalink)
Scorpvenom Registered User Join Date: Dec 2002 Posts: 171 +1 Internets	I think you are wrong. You have your null and alternative hypothesis setup correctly assuming that != means not equal to. The standard deviation should be s and not sigma, but it doesn't really matter how you identify it as long as you plug it into the formula correctly. First, you need to realize that this is a two sided test (due to the fact that your alternative is not equal to), so you want the two tail areas, which are basically symmetric. Find your test statistic either using a z or t distribution, I prefer t, but it shouldn't really matter given the large sample size. T.S. = x bar - mu / (s or sigma / sqr rt of n) I got 22.40 Then using a t or z distribution (doesn't really matter since your n is 30) you get an extremely small p value. I don't have minitab or another program to know the exact p value but an answer of p-val < .01 should be fine. You reject the null hypothesis (Ho). From this data, we are 95% confident (or confident at the 5% level of significance) that the mean Rockwell index for a certain type of steal is different than 75 on average in the population. It appears from the data that the mean average in the population is smaller than 75. __________________ Scorpvenom Overlord

02-15-2006, 12:20 PM	#5 (permalink)
Blaezenfury Registered User Join Date: Jan 2003 Location: Ontario, Canada. Posts: 1,503 +9 Internets	what kind of steel are we talking about? HRPO? CR? flat bar? are you just trying to determine the gauge of the steel? or how much preasure it can take? __________________ Blaezen Feanturi. 65th Halfling OverLord of the Vallon Zek Sever.

02-15-2006, 03:18 PM	#8 (permalink)
Blaezenfury Registered User Join Date: Jan 2003 Location: Ontario, Canada. Posts: 1,503 +9 Internets	I was being serious potam. coffee shut your retarded face, douchebag. __________________ Blaezen Feanturi. 65th Halfling OverLord of the Vallon Zek Sever.

02-15-2006, 05:54 PM	#10 (permalink)
Blaezenfury Registered User Join Date: Jan 2003 Location: Ontario, Canada. Posts: 1,503 +9 Internets	the type of steel OBVIOUSLY FUCKING DETERMINES ITS STATISTICS YOU FUCKING IMBECILE. hi different types of steels are made differently, meaning different chemicles and or different process of making it. HRPO = hot rolled pickled & Oiled. CR = Cold Rolled. etc.. What the fuck kind of retard are you? DURRR THE TYPE OF BREAD DOESENT DETERMIN ITS CALORIES/SODIUM/CARBS! HAW HAW DURR. seriously you stupid cunt, dont ever fucking put your mouth where it doesen't belong. it'll get your ass owned. __________________ Blaezen Feanturi. 65th Halfling OverLord of the Vallon Zek Sever.

02-14-2006, 02:32 PM	#2 (permalink)
aeradyn doesn't get it Join Date: Apr 2003 Location: Canada Posts: 130 +0 Internets	Ah got it I think. 0.0969?

02-15-2006, 12:17 PM	#4 (permalink)
BruuceWarduck Banned Join Date: Dec 2002 Location: Banned.... SIKE! Posts: 811 +0 Internets	i got 33.062

02-15-2006, 04:14 PM	#9 (permalink)
GrobbeeTrull Banned Join Date: Oct 2002 Location: Springfield, Ohio Posts: 1,685 +0 Internets	Blaezen, the type of steel doesn't matter, because we're not trying to find the type of steel. We're trying to determine STATISTICS.

02-15-2006, 07:13 PM	#11 (permalink)
Ibliss Registered User Join Date: Jan 2004 Location: Chicago Posts: 285 +0 Internets	Dude, seriously...its a fucking stat problem. It really doesnt matter what kind of steel they are describing. They could be talking about Jello and it wouldnt matter.

02-15-2006, 08:33 PM	#12 (permalink)
Duppin Registered User Join Date: Aug 2002 Posts: 4,466 -17 Internets	My god. This thread really drives home why people make fun of Blaezenfury. I have never seen more determined ignorance in my life.

02-16-2006, 08:09 AM	#14 (permalink)
Eomer You mean I can change this? Neat! Join Date: Feb 2002 Posts: 10,202 +39 Internets	Intentional or not, Blaezen ought to go down in internet history as one of the most effective trolls of all time.

02-16-2006, 09:30 AM	#15 (permalink)
Belefuu Poster Heavy Join Date: May 2002 Posts: 1,000 -2 Internets	Well if it's not intentional, then he wouldn't be a troll now would he? He would just be a retard. I think we're all pretty sure it's not intentional.

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