Probability density question

genericname · 2012-10-20 10:51:29

Given a random variable X with probability density f(x) = x/8 for 0 ≤ x ≤ 4:
1) What is the probability that X is between 1 and 3?
2) Find the expected value of X

How do you find the expected value for these type of questions? In general to find the expected value you use (x*(p(x)), so does that mean you have to plug in numbers 0 to 4 and apply the same formula after? Also for number 1 I got 1/2 as an answer.

Last edited by genericname (2012-10-20 11:04:07)

bobbym · 2012-10-20 11:07:58

Hi;

I am getting that for 1 also, for 2) I am getting 8 / 3.

genericname · 2012-10-20 11:22:42

What is the formula for getting 8/3?

bobbym · 2012-10-20 11:26:10

I did it this way:

genericname · 2012-10-20 11:42:39

I'm not quite understanding it. The value of x = 0, 1, 2, 3, 4?

bobbym · 2012-10-20 11:45:31

Nope, the value of x is those and everything in between them. This is a continuous function.

genericname · 2012-10-20 11:51:38

How does it come up to 8/3? (Sorry for the dumb questions)

bobbym · 2012-10-20 11:59:42

Hi;

Did you see post #4? That is the formula. I just took the endpoints from the problem.

genericname · 2012-10-20 12:13:31

Ah, thank you. I was overthinking it.

bobbym · 2012-10-20 12:15:59

Hi;

Or maybe I am underthinking it. Anyway, hope that helps a little.

Math Is Fun Forum

#1 2012-10-20 10:51:29

Probability density question

#2 2012-10-20 11:07:58

Re: Probability density question

#3 2012-10-20 11:22:42

Re: Probability density question

#4 2012-10-20 11:26:10

Re: Probability density question

#5 2012-10-20 11:42:39

Re: Probability density question

#6 2012-10-20 11:45:31

Re: Probability density question

#7 2012-10-20 11:51:38

Re: Probability density question

#8 2012-10-20 11:59:42

Re: Probability density question

#9 2012-10-20 12:13:31

Re: Probability density question

#10 2012-10-20 12:15:59

Re: Probability density question

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