Math Help Forum - Basic Statistics and Probability

probability 1

mhitch03 — Fri, 20 Nov 2009 17:27:32 GMT

Can anyone help me with this problem? Thanks in advance.

A random variable X has {1,3,6} as only possible values. E(x) = 4 and Var(x) = 2. Find Pr (4=1), Pr (4=3), Pr (4=6) or explain why no such variable exists.

Mean and Standard deviation.

CURRTIS — Fri, 20 Nov 2009 14:09:39 GMT

Just wondering if anyone could point me in the right direction, I need to decide what distribution method to use.

'Recent work at a particular environmental monitoring station shows thath ourly concentrations of an airborne pollutant has mean 26.01 ml/m^3 and standard deviation 7.342ml/m^3.In selecting a suitable distribution note that, under exceptional environmental conditions, concentrations of pollutants can be very large.'

Probability Density of Normal Distribution

kburk46 — Fri, 20 Nov 2009 03:09:34 GMT

Suppose X has normal (μ,σ^2) distribution, and P(X≤0)=1/3, P(X≤1)=2/3.
a) What are the values of μ and σ?
b) What if instead P(X≤1)=3/4?

Independence Question - Can anyone check my solution please?

essedra — Thu, 19 Nov 2009 23:37:37 GMT

Your computer has been acting very strangely lately, and you suspect that it might have a virus on it. Unfortunately, all 15 of the different virus detection programs you own are outdated. You know that if your computer does have a virus, each of the programs, independently of the others, has a 0.77 chance of believing that your computer as infected, and a 0.23 chance of thinking your computer is fine. On the other hand, if your computer does not have a virus, each program has a 0.93 chance of believing that your computer is fine, and a 0.07 chance of wrongly thinking your computer is infected. Given that your computer has a 0.64 chance of being infected with some virus, and given that you will believe your virus protection programs only if 11 or more of them agree, find the probability that your detection programs will lead you to the right answer.

Exponential distribution

rateesh — Thu, 19 Nov 2009 22:45:40 GMT

Hi all,

Having difficulty understanding the exponential distribution. Could someone help me understand this.

rateesh

please help in selecting the events of probability

sgk1980 — Thu, 19 Nov 2009 16:48:13 GMT

I have the following probability assesment table
no.of blemishes-0,1,2,3,4,5
probability-0.34,0.25,0.19,0.11,0.07,0.04

I was trying to select an event A i.e more than 2 blemishes and event B which is 4 or fewer blemishes.

means P(A>=2) and P(B<=4) inorder to calculate P(A) & P(B)how should I approach?Do I need proceed thru binomial distribution?

Thanks In advance

Continuous Probability Distributions

hazel — Thu, 19 Nov 2009 15:51:24 GMT

3.27 walpole

The time to failure in hours of an important piece of electronic equipment used in a manufactured DVD player has the density function

f(x) = 1/2000 exp (-x/2000), x>=0
0, x<0

find F(x).

my queries :
- so meaning integrate from 0 to x or 0 to infinity ?
- and could i use du=-x/2000 dx to solve ? i saw some of my mates using dt. which i don't know how does dt fit in . (Thinking)

pls advise. thks!

Can someone please explain how to compute the mean and standard deviation for this qu

Ttops — Thu, 19 Nov 2009 15:13:56 GMT

I wasnt sure where to post this question but since it`s stats, i decided to post it here.

p(x)=(1/4)(3/4)^(x-1), X=1,2,3,4

I'm totally confused on how to do it...the question and answer is in the word.doc provided but i need an explanation on how the answer is created.
Thank you.

Attached Files

worksheet question.doc (23.5 KB)

random variable???

leefuqua05 — Thu, 19 Nov 2009 05:23:39 GMT

Let be a standard normal random variable. Use the calculator provided to determine the value of such that .

Carry your intermediate computations to at least four decimal places. Round your answer to at least two decimal places.

Need help in variable

leefuqua05 — Thu, 19 Nov 2009 03:34:49 GMT

Let be a standard normal random variable. Determine the value of such that

Need quick help for intermediate computation

leefuqua05 — Thu, 19 Nov 2009 03:32:30 GMT

A newspaper article reported that people spend a mean of hours per day watching TV, with a standard deviation of hours. A psychologist would like to conduct interviews with the of the population who spend the most time watching TV. She assumes that the daily time people spend watching TV is normally distributed. At least how many hours of daily TV watching are necessary for a person to be eligible for the interview? Carry your intermediate computations to at least four decimal places. Round your answer to at least one decimal place.

i'm absoultley horrible with this and i am a bit confused as far as the hours go... i would appreciate any help thanks

How to find the period of the time series

[nuthing] — Thu, 19 Nov 2009 01:37:19 GMT

Hi, I was wondering whether anyone knew how to figure out what moving average was in a time series data. eg. 3 point moving average. (Angry)
thank you

Finding Sample size? (Normal Distribution)

superjen — Thu, 19 Nov 2009 00:58:19 GMT

I'm not really sure what to name this, and im pretty sure it belongs here, im sorry if it doesnt.

Question

The number of loaves of white bread demanded daily at a bakery is normally distributed with mean 6800 loaves and variance 84000. the company decides to produce a sufficient number of loaves so that it will fully supply demand on 95% of the days.

(a) How many loaves of bread should the compan produce?

I know i need to find n = CI * standard dev. / E .. i can figure out CI and SD. but i cant find E..

(b) Based on (a), on what percentage of days will the company be left with more than 500 loaves of unsold bread?

I'm not sure on how to do this one!

Any amount of help would be amazing!!

More expected value

Twig — Wed, 18 Nov 2009 23:27:21 GMT

Hi!

A family has children until it has a boy or until it has three children, whichever comes first. Assume the child is a boy with probability . Find the expected number of boys in this family, and the expected number of girls.

Let denote the number of boys in the family.
Let denote the number of girls in the family.

We are seeking and .

There are the following possible "child outcomes": G = girl B = boy

It is not possible to have for example BBG, since the family stops having children when they have gotten a boy.
Let be any of the events in .
Hence,

Did I go wrong somewhere, if so, what is the error?

Thanks!

Expected Value

Twig — Wed, 18 Nov 2009 23:00:14 GMT

Hi!

Problem: A die is rolled twice. Let denote the sum of the two numbers that turn up, and the difference of the numbers (specifically, the number on the first roll minus the number on the second roll). Show that

Are and independant?

Thanks