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#1 2013-10-03 23:04:52

puccinitang
Guest

Probability

dunno Help me plz, thanks wink

A teacher claims that the time (in minutes) required for any HKU student to finish the homework is a normally distributed random variable with a mean of 30 minutes and a standard deviation of 10 minutes.

(i) If a student is randomly selected from HKU, what is the probability that he/she will use more than 27 minutes but less than 32 minutes to finish the homework?

(ii) If a sample of 6 students is randomly selected from HKU, find the probability that the average time of 6 students to finish the homework will be more than 32 minutes?

(iii) Suppose the time (in minutes) required to finish the homework is not a normal random variable. Under what circumstances can part (b) still be evaluated?

#2 2013-10-03 23:09:03

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 82,753

Re: Probability

Hi;

i) P(27 < X <= 32) = .1972

Under what circumstances can part (b) still be evaluated?

Where is part b?


In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

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#3 2013-10-05 16:53:07

puccinitang
Guest

Re: Probability

sorry, part b= part ii

#4 2013-10-05 21:11:24

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 82,753

Re: Probability

Hi;

ii) .3121


In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

Online

#5 2013-10-06 04:40:24

puccinitang
Guest

Re: Probability

how about iii?
help me please /_\

#6 2013-10-06 10:19:25

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 82,753

Re: Probability

Hi;

iii) The question is way too general and requires making too many assumptions. If I draw at random from a distribution of any shape and I draw a big sample then the distribution of the sample will approach a normal distribution. They usually pick n = 30.

If I draw a sample of 6 students from this unknown distribution then I will have great difficulty with ii)

The general answer for iii) is that I can get the answer if I know the distribution or if the random sample is 30 or more. This is the best I can do.


In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

Online

#7 2013-10-07 06:27:53

puccinitang
Guest

Re: Probability

thank you very much wink

#8 2013-10-07 06:34:52

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 82,753

Re: Probability

Hi;

Hope that was okay and welcome to the forum.


In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

Online

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