How do I evaluate this Poisson distribution?

[KAISER91]

Homework Statement

How do I evaluate this Poisson distribution?

Homework Equations

The Attempt at a Solution

So I have figured out what the values for lambda and x are, but I don't know how to evaluate once I plug the values into the formula.


λ = 20
x = 18

= [ e^-20 x 20^18 ] / 18!


exp -20 x 20^18 is easy to find but how do plug in 18 factorial in the calculator?

 

[micromass]

Simple do 18.17.16.15.14.13.12.11.10.9.8.7.6.5.4.3.2

 

[KAISER91]

Simple do 18.17.16.15.14.13.12.11.10.9.8.7.6.5.4.3.2

I'm not sure what you mean.



The answer to the question is 0.0844

 

[micromass]

What does 18! mean?

 

[KAISER91]

What does 18! mean?

I think it simply means the factorial of 18

It's from the Poisson probability distribution formula, which is;



f (x) = (e^-lambda x lambda^x ) / x!


And I just plugged in the values of x and lambda


I'm not sure how to evaluate this

 

[Char. Limit]

Well, there is usually a factorial button in your calculator, somewhere.

Try under the MATH menu.

 

[micromass]

What does the factorial of 18 mean?

It just means 18!=18.17.16.15.14.13.12.11.10.9.8.7.6.5.4.3.2.1

Calculate it like that...

 

[KAISER91]

Well, there is usually a factorial button in your calculator, somewhere.

Try under the MATH menu.

I have tried that several times but keep coming up with the wrong answer.

LOLI think it may be something else I'm doing wrong.e^-20 simply means the exponential of -20 ? right??

 

[KAISER91]

Well, there is usually a factorial button in your calculator, somewhere.

Try under the MATH menu.

Yep, I see the factorial button.

I'm using a CASIO 100 so it's simply shift + x^-1 on the calculator.

 

[Char. Limit]

Well, your formula should be correct. Are you sure your x and $\lambda$ values are correct?

 

[KAISER91]

Well, your formula should be correct. Are you sure your x and $\lambda$ values are correct?

Yes I'm sure.

Let me take a screenshot of it for you.

 

[KAISER91]

http://oi53.tinypic.com/68su2o.jpg"

This is the worked answer given

 

[Char. Limit]

Well, I get the same answer as the book, so your calculations must be wrong somewhere.

 

[KAISER91]

Yep.

Nevermind, I have found out my problem.

I was using the wrong button on the calculator for exponential.

LOL