Math Is Fun Forum

van364

Member

Registered: 2011-11-06

Posts: 13

Statistics Help

I need help on one of these questions can anyone break this problem down step by step and explain to me how this works:
Based on data from the National Health and Nutrition Examination Survery, assume that weights of men are normally distributed with a mean of 172lbs and a Standard deviation of 29lbs.

a)Find the probability that is an individual man is randomly selected his weight will be greater then 180lbs.

b)Find the probability that 20 RANDOMLY SELECTED MEN will have a mean weight that is greater then 180lbs.

c)If 20 men have a mean weight greater then 180lbs, and the total weight exceeds the 3500lb safe capacity of a particular water taxi. Based on the preceding results, is this a safety concern? Why or why not?

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Statistics Help

Hi;

First you get a z score:

What do you get for that?

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

van364

Member

Registered: 2011-11-06

Posts: 13

Re: Statistics Help

I got .2759

van364

Member

Registered: 2011-11-06

Posts: 13

Re: Statistics Help

okay from there i put in normalcdf(.2759,5) and i would get .3913

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Statistics Help

That is correct!

Go here:

http://www.measuringusability.com/pcalc … .35&side=1

There you will find a z score calculator. Tell me when you are there.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

van364

Member

Registered: 2011-11-06

Posts: 13

Re: Statistics Help

okay i'm there

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Statistics Help

Enter .2759 in the zscore box. 4 decimal points and check one sided and press submit.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

van364

Member

Registered: 2011-11-06

Posts: 13

Re: Statistics Help

okay what would both percentages stand for?

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Statistics Help

The one on the right is what you are interested in because this is a one tailed test. Greater than 180 lbs is one tailed. It agrees with your answer.

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

van364

Member

Registered: 2011-11-06

Posts: 13

Re: Statistics Help

ohhh i see. Now for the second one how do i do that now that i have 20 people?

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Statistics Help

Hi van364;

I am a little confused on that one myself. To know the probability of 20 randomly selected people I need to know how many people were selected, 20, 25, 100, 1000...

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

van364

Member

Registered: 2011-11-06

Posts: 13

Re: Statistics Help

hmmm lets say its 25 people, how would we find that?

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Statistics Help

Hold on! I am working on the problem.

b) Is a t score. Do you know how to do them?

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

van364

Member

Registered: 2011-11-06

Posts: 13

Re: Statistics Help

never done t-scores before, how do we do them?

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Statistics Help

b)Find the probability that 20 RANDOMLY SELECTED MEN will have a mean weight that is greater then 180lbs.

We compute it like this:

What do you get for t(180)?

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

van364

Member

Registered: 2011-11-06

Posts: 13

Re: Statistics Help

okay i got the second one by using a different formula getting a z score of 1.23, then i put it in normalcdf(1.23,5) and got .1093 as the answer

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Statistics Help

Are you working on b?

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

van364

Member

Registered: 2011-11-06

Posts: 13

Re: Statistics Help

yes i found out the answer thanks to the formula you gave me earlier, and i figured out C based on the information B provided. thank you!

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Statistics Help

Hi;

Your welcome but are you sure b) is a normal distribution problem? I think it is a t-score like in post #15. I am getting .1169 as the probability.

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

van364

Member

Registered: 2011-11-06

Posts: 13

Re: Statistics Help

yep its under the normal probability distribution chapter review lol

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Statistics Help

We are talking about the original question b? Can I see your working?

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.