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Matt
science forum beginner
Joined: 24 Dec 2005
Posts: 25
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 Posted: Sat May 20, 2006 5:27 pm Post subject:
Stastics Question
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A recent study found that the average life expectancy of a person
living in Africa is 53 years with a standard deviation of 7.5 years.
If a person in Africa is selected at random, what is the probability
that the person will die before the age of 65?
a. 93.45%
b. 82.89%
c. 94.95%
d. 88.49%
Thanks everyone for your help!
Best wishes!
Matt |
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Virgil
science forum Guru
Joined: 24 Mar 2005
Posts: 5536
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| Posted: Sat May 20, 2006 5:49 pm Post subject:
Re: Stastics Question
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In article <1148146062.912968.27360@y43g2000cwc.googlegroups.com>,
"Matt" <matthewamack@yahoo.com> wrote:
| Quote: | A recent study found that the average life expectancy of a person
living in Africa is 53 years with a standard deviation of 7.5 years.
If a person in Africa is selected at random, what is the probability
that the person will die before the age of 65?
a. 93.45%
b. 82.89%
c. 94.95%
d. 88.49%
Thanks everyone for your help!
Best wishes!
Matt
|
In a standard normal distribution, z, with mean 0 and standard
deviation 1, what is the probability that z < (65-53)/7.5 ? |
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Brian M. Scott
science forum Guru
Joined: 10 May 2005
Posts: 332
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| Posted: Sat May 20, 2006 5:54 pm Post subject:
Re: Stastics Question
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On 20 May 2006 10:27:42 -0700, Matt <matthewamack@yahoo.com>
wrote in
<news:1148146062.912968.27360@y43g2000cwc.googlegroups.com>
in alt.math.undergrad:
| Quote: | A recent study found that the average life expectancy of a person
living in Africa is 53 years with a standard deviation of 7.5 years.
If a person in Africa is selected at random, what is the probability
that the person will die before the age of 65?
|
65 is 12 years above the mean, so it's 12/7.5 = 1.6 standard
deviations above the mean. Any standard table of the normal
distribution will tell you what percentage of the area under
the normal curve lies to the left of z = 1.6. (With some
you may have to do a *little* more work: some will tell you
the percentage of area between z = -1.6 and z = 1.6 instead,
and you'll have to calculate and add in the area of the
lefthand tail.)
[...]
Brian |
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Stan Brown
science forum Guru Wannabe
Joined: 06 May 2005
Posts: 279
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| Posted: Sat May 20, 2006 9:29 pm Post subject:
Re: Stastics Question
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Sat, 20 May 2006 11:49:12 -0600 from Virgil <vmhjr2@comcast.net>:
| Quote: | In article <1148146062.912968.27360@y43g2000cwc.googlegroups.com>,
"Matt" <matthewamack@yahoo.com> wrote:
A recent study found that the average life expectancy of a person
living in Africa is 53 years with a standard deviation of 7.5 years.
If a person in Africa is selected at random, what is the probability
that the person will die before the age of 65?
In a standard normal distribution, z, with mean 0 and standard
deviation 1, what is the probability that z < (65-53)/7.5 ?
|
I have little doubt that's the answer the problem wanted, but it's
worth pointing out that the problem didn't _say_ the ages at death
were normally distributed. (Or else the student didn't copy the
problem completely.)
I wonder: *is* age at death normally distributed? Intuition tells me
it's much more J-shaped, but I don't have any data.
--
Stan Brown, Oak Road Systems, Tompkins County, New York, USA
http://OakRoadSystems.com/ |
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Matt
science forum beginner
Joined: 24 Dec 2005
Posts: 25
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| Posted: Sun May 21, 2006 4:12 pm Post subject:
Re: Stastics Question
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Thanks Stan for your time and help with this problem. That is all the
question asked. I feel some of the questions I am trying to answer are
too vague, but I guess that is why it's multiple choice. Thanks again! |
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Dana DeLouis
science forum beginner
Joined: 06 Mar 2006
Posts: 37
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| Posted: Sun May 21, 2006 10:37 pm Post subject:
Re: Stastics Question
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It's been awhile since I've done these problems...
Is this how it would be done using a spreadsheet program like Excel?
=NORMDIST(65,53,7.5,TRUE)
However, this returns 94.52%, which is not one of the choices. Hmmm.
(Assuming a Norm. Distribution also)
--
Dana
"Matt" <matthewamack@yahoo.com> wrote in message
news:1148227926.838152.232360@g10g2000cwb.googlegroups.com...
| Quote: | Thanks Stan for your time and help with this problem. That is all the
question asked. I feel some of the questions I am trying to answer are
too vague, but I guess that is why it's multiple choice. Thanks again!
|
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Brian M. Scott
science forum Guru
Joined: 10 May 2005
Posts: 332
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| Posted: Sun May 21, 2006 11:05 pm Post subject:
Re: Stastics Question
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On Sun, 21 May 2006 18:37:33 -0400, Dana
<ddelouis@bellsouth.net> wrote in
<news:TY5cg.56781$MM6.48392@bignews3.bellsouth.net> in
alt.math.undergrad:
| Quote: | It's been awhile since I've done these problems...
Is this how it would be done using a spreadsheet program like Excel?
=NORMDIST(65,53,7.5,TRUE)
However, this returns 94.52%, which is not one of the choices. [...]
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That's what I get from standard tables.
Brian |
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