Probability distribution (NEED HELP BIG TIME)

• Apr 10th 2008, 04:53 PM
uni-student
Probability distribution (NEED HELP BIG TIME)
================================================== ======
*PLEASE DON'T simply write the answer, I NEED STEP BY STEP, on how to do it
================================================== ======
question 2
This is a Probability distribution question i don't understand how to answer is, there are 3 questions

In order to verify the accuracy of their financial accounts, companies use auditors on a regular basis to check the accuracy of the accounts entries. The companies accountants make errors in 5% of the entries. If an auditor randomly checks 3 entries, and the random variable Y is the number of errors detected by the auditor, then

a) Find the probability distribution of the random variable Y,

b) Find E(Y) and Var(Y),

c) And the probability that more than one error will be found by the auditor?
• Apr 10th 2008, 05:17 PM
mr fantastic
Quote:

Originally Posted by uni-student
================================================== ======
*PLEASE DON'T simply write the answer, I NEED STEP BY STEP, on how to do it
================================================== ======
question 2
This is a Probability distribution question i don't understand how to answer is, there are 3 questions

In order to verify the accuracy of their financial accounts, companies use auditors on a regular basis to check the accuracy of the accounts entries. The companies accountants make errors in 5% of the entries. If an auditor randomly checks 3 entries, and the random variable Y is the number of errors detected by the auditor, then

a) Find the probability distribution of the random variable Y,
b) Find E(Y) and Var(Y),
c) And the probability that more than one error will be found by the auditor?

Knowing the answer to a) should enable you to answer b) and c).

The answer to a) is that Y follows a binomial distribution with n = 3 and p = 0.05 = 1/20.
• Apr 10th 2008, 05:32 PM
uni-student
okk thanks, i get its now. lol its so simple,

but iam not sure about c)?
• Apr 10th 2008, 06:03 PM
mr fantastic
Quote:

Originally Posted by uni-student
[snip]
In order to verify the accuracy of their financial accounts, companies use auditors on a regular basis to check the accuracy of the accounts entries. The companies accountants make errors in 5% of the entries. If an auditor randomly checks 3 entries, and the random variable Y is the number of errors detected by the auditor, then

c) The probability that more than one error will be found by the auditor?

Please don't edit a question after it's been replied to. It makes it very difficult for others to follow (believe it or not, many folk visit sites like this to read the posted questions and learn from them). In this case it's not too much of a problem because I quoted your original question in my first reply.

c) Pr(Y > 1) = Pr(Y = 2) + Pr(Y = 3).

Alternatively, Pr(Y > 1) = 1 - Pr(Y = 0) - Pr(Y = 1).
• Apr 10th 2008, 08:17 PM
uni-student
ok, sorry, will note in future

and whats the probability of Pr(Y=1), Pr(Y=0), Pr(Y=2) and Pr(Y=3)

iam confused, if n=0.05 therefore q=0.95, but i don't know how solve Pr(Y=...)
• Apr 10th 2008, 09:58 PM
mr fantastic
Quote:

Originally Posted by uni-student
ok, sorry, will note in future

and whats the probability of Pr(Y=1), Pr(Y=0), Pr(Y=2) and Pr(Y=3)

iam confused, if n=0.05 therefore q=0.95, but i don't know how solve Pr(Y=...)

I quote from my first reply:

"Y follows a binomial distribution with n = 3 and p = 0.05 = 1/20."

I don't understand what you're confused about ...... You have studied the binomial distribution, yes?
• Apr 10th 2008, 10:19 PM
uni-student
yes, are u talking about ncr functions?

please just solve it for me step by step so i can learn the things i forgot in year 12 (which is this).
• Apr 10th 2008, 11:07 PM
mr fantastic
Quote:

Originally Posted by uni-student
yes, are u talking about ncr functions?

please just solve it for me step by step so i can learn the things i forgot in year 12 (which is this).

You said earlier that you got it. Now you're saying you can't do a thing.

Sorry, but I'm not doing your work for you.

My last word is that if Y ~ Binomial(n, p), then \$\displaystyle \Pr(Y = r) = \, ^nC _r \, p^r \, (1 - p)^{n-r}\$.